[clang] [C23] Implement WG14 N3037 (PR #132939)

[Erich Keane via cfe-commits]

================
@@ -11399,6 +11400,22 @@ static QualType mergeEnumWithInteger(ASTContext &Context, const EnumType *ET,
   return {};
 }
 
+QualType ASTContext::mergeTagTypes(QualType LHS, QualType RHS) {
----------------
erichkeane wrote:

So this isn't really merging the TYPES, more merging tag-definitions?  Should the name be more accurate?  Because 'merging' two tag types is valid if one isn't a definition otherwise.

https://github.com/llvm/llvm-project/pull/132939