MC: add support for cfi_return_column

This adds support for the CFI pseudo-op return_column.  This specifies
the frame table column which contains the return address.

Addresses PR33953!

llvm-svn: 309360
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index 2bfb9a6..e35907f 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -508,6 +508,12 @@
   CurFrame->Instructions.push_back(Instruction);
 }
 
+void MCStreamer::EmitCFIReturnColumn(int64_t Register) {
+  EnsureValidDwarfFrame();
+  MCDwarfFrameInfo *CurFrame = getCurrentDwarfFrameInfo();
+  CurFrame->RAReg = Register;
+}
+
 void MCStreamer::EnsureValidWinFrameInfo() {
   const MCAsmInfo *MAI = Context.getAsmInfo();
   if (!MAI->usesWindowsCFI())