Use -enable-global-merge option to match llvm r210639. <rdar://problem/17803206>

llvm revision 210639 renamed the -global-merge backend option to
-enable-global-merge. This change simply updates clang to match that.

Patch by Steven Wu!

llvm-svn: 213993
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index a1521dc..cec48f3 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -383,7 +383,7 @@
   for (unsigned i = 0, e = CodeGenOpts.BackendOptions.size(); i != e; ++i)
     BackendArgs.push_back(CodeGenOpts.BackendOptions[i].c_str());
   if (CodeGenOpts.NoGlobalMerge)
-    BackendArgs.push_back("-global-merge=false");
+    BackendArgs.push_back("-enable-global-merge=false");
   BackendArgs.push_back(nullptr);
   llvm::cl::ParseCommandLineOptions(BackendArgs.size() - 1,
                                     BackendArgs.data());