Invoke the Darwin assembler with -g instead of --gdwarf2.

The -g and --gdwarf2 options are currently synonyms to the Darwin assembler.
But clang itself does not recognize --gdwarf2, so if we want to experiment
with using clang, with its integrated assembler, to replace the default
assembler, it is necessary to use -g.  <rdar://problem/10349486>

llvm-svn: 143533

clang/lib/Driver/Tools.cpp

@@ -3130,7 +3130,7 @@ void darwin::Assemble::ConstructJob(Compilation &C, const JobAction &JA,
     if (Args.hasArg(options::OPT_gstabs))
       CmdArgs.push_back("--gstabs");
     else if (Args.hasArg(options::OPT_g_Group))
-      CmdArgs.push_back("--gdwarf2");
+      CmdArgs.push_back("-g");
   }
 
   // Derived from asm spec.