Give isCompatibleWithMSVC a better interface

We now use an enum which maps the marketing name (almost always a year)
to the major version number.

llvm-svn: 236967
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index bc31d46..ac8f576 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3450,8 +3450,9 @@
 // We will pick our mangling number depending on which version of MSVC is being
 // targeted.
 static unsigned getMSManglingNumber(const LangOptions &LO, Scope *S) {
-  return LO.isCompatibleWithMSVC(19) ? S->getMSCurManglingNumber()
-                                     : S->getMSLastManglingNumber();
+  return LO.isCompatibleWithMSVC(LangOptions::MSVC2015)
+             ? S->getMSCurManglingNumber()
+             : S->getMSLastManglingNumber();
 }
 
 void Sema::handleTagNumbering(const TagDecl *Tag, Scope *TagScope) {