[Driver] Pass -f[no-]emulated-tls and set up ExplicitEmulatedTLS

Since LLVM r326341, default EmulatedTLS mode is decided in backend
according to target triple. Any front-end should pass -f[no]-emulated-tls
to backend and set up ExplicitEmulatedTLS only when the flags are used.

Differential Revision: https://reviews.llvm.org/D43965

llvm-svn: 326499
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index dde6577..f2733ce 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -433,6 +433,7 @@
   Options.DataSections = CodeGenOpts.DataSections;
   Options.UniqueSectionNames = CodeGenOpts.UniqueSectionNames;
   Options.EmulatedTLS = CodeGenOpts.EmulatedTLS;
+  Options.ExplicitEmulatedTLS = CodeGenOpts.ExplicitEmulatedTLS;
   Options.DebuggerTuning = CodeGenOpts.getDebuggerTuning();
   Options.EmitStackSizeSection = CodeGenOpts.StackSizeSection;