[cfi] Add flag to always generate .debug_frame

This adds a flag to LLVM and clang to always generate a .debug_frame
section, even if other debug information is not being generated. In
situations where .eh_frame would normally be emitted, both .debug_frame
and .eh_frame will be used.

Differential Revision: https://reviews.llvm.org/D67216
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 75a54d8..c15dc0b 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -485,6 +485,7 @@
   Options.EmitStackSizeSection = CodeGenOpts.StackSizeSection;
   Options.EmitAddrsig = CodeGenOpts.Addrsig;
   Options.EnableDebugEntryValues = CodeGenOpts.EnableDebugEntryValues;
+  Options.ForceDwarfFrameSection = CodeGenOpts.ForceDwarfFrameSection;
 
   Options.MCOptions.SplitDwarfFile = CodeGenOpts.SplitDwarfFile;
   Options.MCOptions.MCRelaxAll = CodeGenOpts.RelaxAll;