compiler-rt: add aarch64 init function for LSE atomics

As reported by Ronald, adding the out-of-line LSE atomics helpers for
aarch64 to compiler-rt was not sufficient to link programs using these,
as they also require a __aarch64_have_lse_atomics global. This is
initialized in compiler-rt's lib/builtins/cpu_model.c, roughly similar
to the x86 CPU model and feature detection in that file.

Since upstream does not yet have a FreeBSD specific implementation for
getting the required information, add a simple one that should work for
now, while I try to get it sorted with the LLVM people.

Reported by:	Ronald Klop <ronald-lists@klop.ws>
Fixes:		cc55ee8009
PR:		257392
MFC after:	2 weeks

contrib/llvm-project/compiler-rt/lib/builtins/cpu_model.c

@@ -775,8 +775,14 @@ _Bool __aarch64_have_lse_atomics
 #define HWCAP_ATOMICS (1 << 8)
 #endif
 static void CONSTRUCTOR_ATTRIBUTE init_have_lse_atomics(void) {
+#if defined(__FreeBSD__)
+  unsigned long hwcap;
+  int result = elf_aux_info(AT_HWCAP, &hwcap, sizeof hwcap);
+  __aarch64_have_lse_atomics = result == 0 && (hwcap & HWCAP_ATOMICS) != 0;
+#else
   unsigned long hwcap = getauxval(AT_HWCAP);
   __aarch64_have_lse_atomics = (hwcap & HWCAP_ATOMICS) != 0;
+#endif
 }
 #endif // defined(__has_include)
 #endif // __has_include(<sys/auxv.h>)

lib/libcompiler_rt/Makefile.inc

@@ -146,8 +146,9 @@ SRCF+=		floatundisf
 SRCF+=		floatundixf
 .endif
 
-# __cpu_model support, only used on x86
-.if ${MACHINE_CPUARCH} == "amd64" || ${MACHINE_CPUARCH} == "i386"
+# __cpu_model support, only used on aarch64 and x86
+.if ${MACHINE_CPUARCH} == "aarch64" || ${MACHINE_CPUARCH} == "amd64" || \
+    ${MACHINE_CPUARCH} == "i386"
 SRCF+=		cpu_model
 .endif