add support for non-standard name of stdc++ library

it makes rustc compatible with gcc installation that are using
`--program-transform-name' configure flag (on OpenBSD for example).

- detects at configure the name of stdc++ library on the system

- use the detected name in llvm makefile (with enable-static-stdcpp),
  and pass it to mklldeps.py

- generate mklldeps.rs using this detected name

note that CFG_STDCPP_NAME is about stdc++ name, not about libc++. If
using libc++, the default name will be `stdc++', but it won't be used
when linking.

configure

@@ -1095,6 +1095,12 @@ envopt CPP
 envopt CFLAGS
 envopt CXXFLAGS
 
+# stdc++ name in use
+# used to manage non-standard name (on OpenBSD for example)
+program_transform_name=$($CFG_CC -v 2>&1 | sed -n "s/.*--program-transform-name='\([^']*\)'.*/\1/p")
+CFG_STDCPP_NAME=$(echo "stdc++" | sed "${program_transform_name}")
+putvar CFG_STDCPP_NAME
+
 # a little post-processing of various config values
 CFG_PREFIX=${CFG_PREFIX%/}
 CFG_MANDIR=${CFG_MANDIR%/}

mk/llvm.mk

@@ -73,7 +73,7 @@ $$(LLVM_STAMP_$(1)): $(S)src/rustllvm/llvm-auto-clean-trigger
 
 ifeq ($$(CFG_ENABLE_LLVM_STATIC_STDCPP),1)
 LLVM_STDCPP_RUSTFLAGS_$(1) = -L "$$(dir $$(shell $$(CC_$(1)) $$(CFG_GCCISH_CFLAGS_$(1)) \
-					-print-file-name=libstdc++.a))"
+					-print-file-name=lib$(CFG_STDCPP_NAME).a))"
 else
 LLVM_STDCPP_RUSTFLAGS_$(1) =
 endif
@@ -83,7 +83,7 @@ endif
 LLVM_LINKAGE_PATH_$(1):=$$(abspath $$(RT_OUTPUT_DIR_$(1))/llvmdeps.rs)
 $$(LLVM_LINKAGE_PATH_$(1)): $(S)src/etc/mklldeps.py $$(LLVM_CONFIG_$(1))
 	$(Q)$(CFG_PYTHON) "$$<" "$$@" "$$(LLVM_COMPONENTS)" "$$(CFG_ENABLE_LLVM_STATIC_STDCPP)" \
-		$$(LLVM_CONFIG_$(1))
+		$$(LLVM_CONFIG_$(1)) "$(CFG_STDCPP_NAME)"
 endef
 
 $(foreach host,$(CFG_HOST), \

src/etc/mklldeps.py

@@ -17,6 +17,7 @@ f = open(sys.argv[1], 'wb')
 components = sys.argv[2].split() # splits on whitespace
 enable_static = sys.argv[3]
 llvm_config = sys.argv[4]
+stdcpp_name = sys.argv[5]
 
 f.write("""// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
@@ -77,7 +78,7 @@ for lib in out.strip().split(' '):
 out = run([llvm_config, '--cxxflags'])
 if enable_static == '1':
     assert('stdlib=libc++' not in out)
-    f.write("#[link(name = \"stdc++\", kind = \"static\")]\n")
+    f.write("#[link(name = \"" + stdcpp_name + "\", kind = \"static\")]\n")
 else:
     # Note that we use `cfg_attr` here because on MSVC the C++ standard library
     # is not c++ or stdc++, but rather the linker takes care of linking the
@@ -85,7 +86,7 @@ else:
     if 'stdlib=libc++' in out:
         f.write("#[cfg_attr(not(target_env = \"msvc\"), link(name = \"c++\"))]\n")
     else:
-        f.write("#[cfg_attr(not(target_env = \"msvc\"), link(name = \"stdc++\"))]\n")
+        f.write("#[cfg_attr(not(target_env = \"msvc\"), link(name = \"" + stdcpp_name + "\"))]\n")
 
 # Attach everything to an extern block
 f.write("extern {}\n")