[codeview] Use push_macro to avoid conflicts instead of a prefix

Summary:
This prefix was added in r333421, and it changed our dumper output to
say things like "CVRegEAX" instead of just "EAX". That's a functional
change that I'd rather avoid.

I tested GCC, Clang, and MSVC, and all of them support #pragma
push_macro. They don't issue warnings whem the macro is not defined
either.

I don't have a Mac so I can't test the real termios.h header, but I
looked at the termios.h sources online and looked for other conflicts.
I saw only the CR* macros, so those are the ones we work around.

Reviewers: zturner, JDevlieghere

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D50851

llvm-svn: 339907
diff --git a/llvm/lib/DebugInfo/PDB/Native/NativeRawSymbol.cpp b/llvm/lib/DebugInfo/PDB/Native/NativeRawSymbol.cpp
index a4b0295..fbe3348 100644
--- a/llvm/lib/DebugInfo/PDB/Native/NativeRawSymbol.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/NativeRawSymbol.cpp
@@ -188,7 +188,7 @@
 }
 
 codeview::RegisterId NativeRawSymbol::getLocalBasePointerRegisterId() const {
-  return codeview::RegisterId::CVRegEAX;
+  return codeview::RegisterId::EAX;
 }
 
 uint32_t NativeRawSymbol::getLowerBoundId() const {
@@ -248,7 +248,7 @@
 }
 
 codeview::RegisterId NativeRawSymbol::getRegisterId() const {
-  return codeview::RegisterId::CVRegEAX;
+  return codeview::RegisterId::EAX;
 }
 
 uint32_t NativeRawSymbol::getRegisterType() const {