Clang support for -flto=thin.

Summary:
Add clang support for -flto=thin option, which is used to set the
EmitFunctionSummary code gen option on compiles.

Add -flto=full as an alias to the existing -flto.

Add tests to check for proper overriding of -flto variants on the
command line, and convert grep tests to FileCheck.

Reviewers: dexonsmith, joker.eph

Subscribers: davidxl, cfe-commits

Differential Revision: http://reviews.llvm.org/D11908

llvm-svn: 250398

clang/lib/CodeGen/BackendUtil.cpp

@@ -605,8 +605,8 @@ void EmitAssemblyHelper::EmitAssembly(BackendAction Action,
     break;
 
   case Backend_EmitBC:
-    getPerModulePasses()->add(
-        createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists));
+    getPerModulePasses()->add(createBitcodeWriterPass(
+        *OS, CodeGenOpts.EmitLLVMUseLists, CodeGenOpts.EmitFunctionSummary));
     break;
 
   case Backend_EmitLL: