diff --git a/configure b/configure
index 3bad491fee1..1e05d87431c 100755
--- a/configure
+++ b/configure
@@ -6271,37 +6271,6 @@ printf "%s\n" "$wine_cv_cc_m32" >&6; }
       export PKG_CONFIG_LIBDIR
       with_unwind=${with_unwind:-no}
     else
-      if test "x${GCC}" = "xyes"
-      then
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CC supports __builtin_ms_va_list" >&5
-printf %s "checking whether $CC supports __builtin_ms_va_list... " >&6; }
-if test ${wine_cv_builtin_ms_va_list+y}
-then :
-  printf %s "(cached) " >&6
-else $as_nop
-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-#include <stdarg.h>
-int
-main (void)
-{
-void func(__builtin_ms_va_list *args);
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"
-then :
-  wine_cv_builtin_ms_va_list=yes
-else $as_nop
-  wine_cv_builtin_ms_va_list=no
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
-fi
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $wine_cv_builtin_ms_va_list" >&5
-printf "%s\n" "$wine_cv_builtin_ms_va_list" >&6; }
-        test $wine_cv_builtin_ms_va_list != no || as_fn_error $? "You need gcc >= 4.4 or clang >= 3.8 to build Wine as 64-bit." "$LINENO" 5
-      fi
       CC="$CC -m64"
       CXX="$CXX -m64"
       host_cpu="x86_64"
diff --git a/configure.ac b/configure.ac
index 3c976233fa3..6e1b8250cc1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -134,13 +134,6 @@ case $host in
       export PKG_CONFIG_LIBDIR
       with_unwind=${with_unwind:-no}
     else
-      if test "x${GCC}" = "xyes"
-      then
-        AC_CACHE_CHECK([whether $CC supports __builtin_ms_va_list],wine_cv_builtin_ms_va_list,
-            [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <stdarg.h>]], [[void func(__builtin_ms_va_list *args);]])],
-                          [wine_cv_builtin_ms_va_list=yes],[wine_cv_builtin_ms_va_list=no])])
-        test $wine_cv_builtin_ms_va_list != no || AC_MSG_ERROR([You need gcc >= 4.4 or clang >= 3.8 to build Wine as 64-bit.])
-      fi
       CC="$CC -m64"
       CXX="$CXX -m64"
       host_cpu="x86_64"
diff --git a/include/dbgeng.h b/include/dbgeng.h
index 4322eff5302..0193d91eae8 100644
--- a/include/dbgeng.h
+++ b/include/dbgeng.h
@@ -1728,6 +1728,8 @@ DECLARE_INTERFACE_(IDebugSymbols3, IUnknown)
 };
 #undef INTERFACE
 
+#ifdef __ms_va_list
+
 #define INTERFACE IDebugControl
 DECLARE_INTERFACE_(IDebugControl, IUnknown)
 {
@@ -2336,6 +2338,8 @@ DECLARE_INTERFACE_(IDebugControl4, IUnknown)
 };
 #undef INTERFACE
 
+#endif  /* __ms_va_list */
+
 #define INTERFACE IDebugAdvanced
 DECLARE_INTERFACE_(IDebugAdvanced, IUnknown)
 {
diff --git a/include/evntrace.h b/include/evntrace.h
index 2c1c625583d..89a6e2ebe34 100644
--- a/include/evntrace.h
+++ b/include/evntrace.h
@@ -309,7 +309,9 @@ ULONG WINAPI StartTraceW(PTRACEHANDLE,LPCWSTR,PEVENT_TRACE_PROPERTIES);
 #define      StartTrace WINELIB_NAME_AW(StartTrace)
 ULONG WINAPI TraceEvent(TRACEHANDLE,PEVENT_TRACE_HEADER);
 ULONG WINAPIV TraceMessage(TRACEHANDLE,ULONG,LPGUID,USHORT,...);
+#ifdef __ms_va_list
 ULONG WINAPI TraceMessageVa(TRACEHANDLE,ULONG,LPGUID,USHORT,__ms_va_list);
+#endif
 ULONG WINAPI UnregisterTraceGuids(TRACEHANDLE);
 
 #ifdef __cplusplus
diff --git a/include/shlwapi.h b/include/shlwapi.h
index e81e9f0e1ec..15615786c4a 100644
--- a/include/shlwapi.h
+++ b/include/shlwapi.h
@@ -945,9 +945,11 @@ WINSHLWAPI BOOL WINAPI StrTrimA(LPSTR,LPCSTR);
 WINSHLWAPI BOOL WINAPI StrTrimW(LPWSTR,LPCWSTR);
 #define StrTrim WINELIB_NAME_AW(StrTrim)
 
+#ifdef __ms_va_list
 WINSHLWAPI INT WINAPI wvnsprintfA(LPSTR,INT,LPCSTR,__ms_va_list);
 WINSHLWAPI INT WINAPI wvnsprintfW(LPWSTR,INT,LPCWSTR,__ms_va_list);
 #define wvnsprintf WINELIB_NAME_AW(wvnsprintf)
+#endif
 
 WINSHLWAPI INT WINAPIV wnsprintfA(LPSTR,INT,LPCSTR, ...);
 WINSHLWAPI INT WINAPIV wnsprintfW(LPWSTR,INT,LPCWSTR, ...);
diff --git a/include/winbase.h b/include/winbase.h
index 13f9f6d9dcb..6d53d9aad86 100644
--- a/include/winbase.h
+++ b/include/winbase.h
@@ -2116,9 +2116,11 @@ WINBASEAPI BOOL        WINAPI FlushFileBuffers(HANDLE);
 WINBASEAPI BOOL        WINAPI FlushInstructionCache(HANDLE,LPCVOID,SIZE_T);
 WINBASEAPI VOID        WINAPI FlushProcessWriteBuffers(void);
 WINBASEAPI BOOL        WINAPI FlushViewOfFile(LPCVOID,SIZE_T);
+#ifdef __ms_va_list
 WINBASEAPI DWORD       WINAPI FormatMessageA(DWORD,LPCVOID,DWORD,DWORD,LPSTR,DWORD,__ms_va_list*);
 WINBASEAPI DWORD       WINAPI FormatMessageW(DWORD,LPCVOID,DWORD,DWORD,LPWSTR,DWORD,__ms_va_list*);
 #define                       FormatMessage WINELIB_NAME_AW(FormatMessage)
+#endif
 WINBASEAPI BOOL        WINAPI FreeEnvironmentStringsA(LPSTR);
 WINBASEAPI BOOL        WINAPI FreeEnvironmentStringsW(LPWSTR);
 #define                       FreeEnvironmentStrings WINELIB_NAME_AW(FreeEnvironmentStrings)
diff --git a/include/windef.h b/include/windef.h
index 366a195febd..cce3dbb36f4 100644
--- a/include/windef.h
+++ b/include/windef.h
@@ -56,37 +56,38 @@ extern "C" {
 
 #if !defined(_MSC_VER) && !defined(__MINGW32__)
 
+#undef __stdcall
+#undef __cdecl
+#undef __fastcall
+#undef __thiscall
+
 #ifdef WINE_UNIX_LIB
 # define __stdcall
 # define __cdecl
-# undef __fastcall
-#else
-# undef __stdcall
+#elif defined(__GNUC__)
 # ifdef __i386__
-#  ifdef __GNUC__
-#   if (__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 2)) || defined(__APPLE__)
-#    define __stdcall __attribute__((__stdcall__)) __attribute__((__force_align_arg_pointer__))
-#   else
-#    define __stdcall __attribute__((__stdcall__))
-#   endif
+#  if (__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 2)) || defined(__APPLE__)
+#   define __stdcall __attribute__((__stdcall__)) __attribute__((__force_align_arg_pointer__))
 #  else
-#   error You need to define __stdcall for your compiler
+#   define __stdcall __attribute__((__stdcall__))
 #  endif
-# elif defined(__x86_64__) && defined (__GNUC__)
+# elif defined(__x86_64__)
 #  if __has_attribute(__force_align_arg_pointer__)
 #   define __stdcall __attribute__((ms_abi)) __attribute__((__force_align_arg_pointer__))
 #  else
 #   define __stdcall __attribute__((ms_abi))
 #  endif
-# elif defined(__arm__) && defined (__GNUC__) && !defined(__SOFTFP__) && !defined(__CYGWIN__)
-#   define __stdcall __attribute__((pcs("aapcs-vfp")))
-# elif defined(__aarch64__) && defined (__GNUC__) && __has_attribute(ms_abi)
+#  define __ms_va_list __builtin_ms_va_list
+# elif defined(__arm__) && !defined(__SOFTFP__) && !defined(__CYGWIN__)
+#  define __stdcall __attribute__((pcs("aapcs-vfp")))
+#  define WINAPIV __attribute__((pcs("aapcs")))
+# elif defined(__aarch64__) && __has_attribute(ms_abi)
 #  define __stdcall __attribute__((ms_abi))
+#  define __ms_va_list __builtin_ms_va_list
 # else  /* __i386__ */
 #  define __stdcall
 # endif  /* __i386__ */
-# undef __cdecl
-# if defined(__i386__) && defined(__GNUC__)
+# ifdef __i386__
 #  if (__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 2)) || defined(__APPLE__)
 #   define __cdecl __attribute__((__cdecl__)) __attribute__((__force_align_arg_pointer__))
 #  else
@@ -95,38 +96,16 @@ extern "C" {
 # else
 #  define __cdecl __stdcall
 # endif
-# ifndef __fastcall
-#  define __fastcall __stdcall
-# endif
-# ifndef __thiscall
-#  define __thiscall __stdcall
-# endif
+# define __fastcall __stdcall
+# define __thiscall __stdcall
+#elif !defined(RC_INVOKED)
+# error You need to define __stdcall for your compiler
 #endif  /* WINE_UNIX_LIB */
 
 #endif  /* _MSC_VER || __MINGW32__ */
 
-#ifndef __ms_va_list
-# if (defined(__x86_64__) || (defined(__aarch64__) && __has_attribute(ms_abi))) && defined (__GNUC__)
-#  define __ms_va_list __builtin_ms_va_list
-#  define __ms_va_start(list,arg) __builtin_ms_va_start(list,arg)
-#  define __ms_va_end(list) __builtin_ms_va_end(list)
-#  define __ms_va_copy(dest,src) __builtin_ms_va_copy(dest,src)
-# else
-#  define __ms_va_list va_list
-#  define __ms_va_start(list,arg) va_start(list,arg)
-#  define __ms_va_end(list) va_end(list)
-#  ifdef va_copy
-#   define __ms_va_copy(dest,src) va_copy(dest,src)
-#  else
-#   define __ms_va_copy(dest,src) ((dest) = (src))
-#  endif
-# endif
-#endif
-
-#if defined(__arm__) && defined (__GNUC__) && !defined(__SOFTFP__) && !defined(__MINGW32__) && !defined(__CYGWIN__)
-# define WINAPIV __attribute__((pcs("aapcs")))
-#else
-# define WINAPIV __cdecl
+#if !defined(__ms_va_list) && !defined(WINE_UNIX_LIB)
+# define __ms_va_list va_list
 #endif
 
 #ifdef __WINESRC__
@@ -142,9 +121,6 @@ extern "C" {
 #ifndef _fastcall
 #define _fastcall   __ONLY_IN_WINELIB(__stdcall)
 #endif
-#ifndef __fastcall
-#define __fastcall  __ONLY_IN_WINELIB(__stdcall)
-#endif
 #ifndef cdecl
 #define cdecl       __ONLY_IN_WINELIB(__cdecl)
 #endif
@@ -202,6 +178,9 @@ extern "C" {
 #define _CDECL      __cdecl
 #define APIENTRY    WINAPI
 #define CONST       __ONLY_IN_WINELIB(const)
+#ifndef WINAPIV
+# define WINAPIV CDECL
+#endif
 
 /* Misc. constants. */
 
diff --git a/include/winternl.h b/include/winternl.h
index 16829442982..faa8621c152 100644
--- a/include/winternl.h
+++ b/include/winternl.h
@@ -4567,8 +4567,10 @@ NTSYSAPI NTSTATUS  WINAPI RtlFlsFree(ULONG);
 NTSYSAPI NTSTATUS  WINAPI RtlFlsGetValue(ULONG,void **);
 NTSYSAPI NTSTATUS  WINAPI RtlFlsSetValue(ULONG,void *);
 NTSYSAPI NTSTATUS  WINAPI RtlFormatCurrentUserKeyPath(PUNICODE_STRING);
+#ifdef __ms_va_list
 NTSYSAPI NTSTATUS  WINAPI RtlFormatMessage(LPCWSTR,ULONG,BOOLEAN,BOOLEAN,BOOLEAN,__ms_va_list *,LPWSTR,ULONG,ULONG*);
 NTSYSAPI NTSTATUS  WINAPI RtlFormatMessageEx(LPCWSTR,ULONG,BOOLEAN,BOOLEAN,BOOLEAN,__ms_va_list *,LPWSTR,ULONG,ULONG*,ULONG);
+#endif
 NTSYSAPI void      WINAPI RtlFreeActivationContextStack(ACTIVATION_CONTEXT_STACK *);
 NTSYSAPI void      WINAPI RtlFreeAnsiString(PANSI_STRING);
 NTSYSAPI BOOLEAN   WINAPI RtlFreeHandle(RTL_HANDLE_TABLE *,RTL_HANDLE *);
@@ -4863,8 +4865,10 @@ NTSYSAPI void      WINAPI TpWaitForIoCompletion(TP_IO *,BOOL);
 NTSYSAPI void      WINAPI TpWaitForTimer(TP_TIMER *,BOOL);
 NTSYSAPI void      WINAPI TpWaitForWait(TP_WAIT *,BOOL);
 NTSYSAPI void      WINAPI TpWaitForWork(TP_WORK *,BOOL);
+#ifdef __ms_va_list
 NTSYSAPI NTSTATUS  WINAPI vDbgPrintEx(ULONG,ULONG,LPCSTR,__ms_va_list);
 NTSYSAPI NTSTATUS  WINAPI vDbgPrintExWithPrefix(LPCSTR,ULONG,ULONG,LPCSTR,__ms_va_list);
+#endif
 
 /* 32-bit or 64-bit only functions */
 
diff --git a/include/winuser.h b/include/winuser.h
index 1d0455c8adf..453f561e62f 100644
--- a/include/winuser.h
+++ b/include/winuser.h
@@ -4682,9 +4682,11 @@ WINUSERAPI VOID        WINAPI mouse_event(DWORD,DWORD,DWORD,DWORD,ULONG_PTR);
 WINUSERAPI INT        WINAPIV wsprintfA(LPSTR,LPCSTR,...);
 WINUSERAPI INT        WINAPIV wsprintfW(LPWSTR,LPCWSTR,...);
 #define                       wsprintf WINELIB_NAME_AW(wsprintf)
+#ifdef __ms_va_list
 WINUSERAPI INT         WINAPI wvsprintfA(LPSTR,LPCSTR,__ms_va_list);
 WINUSERAPI INT         WINAPI wvsprintfW(LPWSTR,LPCWSTR,__ms_va_list);
 #define                       wvsprintf WINELIB_NAME_AW(wvsprintf)
+#endif
 
 #if !defined(__WINESRC__) || defined(WINE_NO_INLINE_RECT)