Re-land "Fix Bug 30978 by emitting cv file checksums."

This reverts r313431 and brings back r313374 with a fix to write
checksums as binary data and not ASCII hex strings.

llvm-svn: 313657

llvm/lib/MC/MCObjectStreamer.cpp

@@ -426,6 +426,9 @@ void MCObjectStreamer::EmitCVFileChecksumsDirective() {
   getContext().getCVContext().emitFileChecksums(*this);
 }
 
+void MCObjectStreamer::EmitCVFileChecksumOffsetDirective(unsigned FileNo) {
+  getContext().getCVContext().emitFileChecksumOffset(*this, FileNo);
+}
 
 void MCObjectStreamer::EmitBytes(StringRef Data) {
   MCCVLineEntry::Make(this);