When using -pg targeting OS X 10.8, pass -no_new_main to the linker.

By default on OS X 10.8, we don't link with a crt1.o file and the linker
knows to use _main as the entry point.  But, when compiling with -pg, we
need to link with the gcrt1.o file, and the linker needs to be told to use
the "start" symbol as the entry point.  The -no_new_main linker option does
that last part.  <rdar://problem/11491405>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159683 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Driver/Tools.cpp

@@ -4341,6 +4341,9 @@ void darwin::Link::ConstructJob(Compilation &C, const JobAction &JA,
 
             // darwin_crt2 spec is empty.
           }
+          if (getDarwinToolChain().isTargetMacOS() &&
+              !getDarwinToolChain().isMacosxVersionLT(10, 8))
+            CmdArgs.push_back("-no_new_main");
         } else {
           if (Args.hasArg(options::OPT_static) ||
               Args.hasArg(options::OPT_object) ||

test/Driver/darwin-ld.c

@@ -121,3 +121,8 @@
 // RUN: %clang -target x86_64-apple-darwin12 -### %t.o 2> %t.log
 // RUN: FileCheck -check-prefix=LINK_NO_CRT1 %s < %t.log
 // LINK_NO_CRT1-NOT: crt
+
+// RUN: %clang -target i386-apple-darwin12 -pg -### %t.o 2> %t.log
+// RUN: FileCheck -check-prefix=LINK_PG %s < %t.log
+// LINK_PG: -lgcrt1.o
+// LINK_PG: -no_new_main