Implement .cfi_undefined. Based on a patch from PaX team, updated by
Roman Divacky. I just added the testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168520 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCStreamer.cpp b/lib/MC/MCStreamer.cpp
index afece0b..02e1028 100644
--- a/lib/MC/MCStreamer.cpp
+++ b/lib/MC/MCStreamer.cpp
@@ -367,6 +367,15 @@
   CurFrame->IsSignalFrame = true;
 }
 
+void MCStreamer::EmitCFIUndefined(int64_t Register) {
+  EnsureValidFrame();
+  MCDwarfFrameInfo *CurFrame = getCurrentFrameInfo();
+  MCSymbol *Label = getContext().CreateTempSymbol();
+  EmitLabel(Label);
+  MCCFIInstruction Instruction(MCCFIInstruction::Undefined, Label, Register);
+  CurFrame->Instructions.push_back(Instruction);
+}
+
 void MCStreamer::setCurrentW64UnwindInfo(MCWin64EHUnwindInfo *Frame) {
   W64UnwindInfos.push_back(Frame);
   CurrentW64UnwindInfo = W64UnwindInfos.back();