Revert "[MS] Fix assert handling enum forward decls in hasVisibleDefinition"

This reverts commit e62dc1f.

Reverting as per discussion with the patch author.
This patch causes module import error, but there was no intended
behavior change for code that does not use Microsoft extensions.

Author: rdhindsa14

clang/lib/Sema/SemaType.cpp

@@ -8120,10 +8120,10 @@ bool Sema::hasVisibleDefinition(NamedDecl *D, NamedDecl **Suggested,
   } else if (auto *ED = dyn_cast<EnumDecl>(D)) {
     if (auto *Pattern = ED->getTemplateInstantiationPattern())
       ED = Pattern;
-    if (OnlyNeedComplete && !ED->getIntegerType().isNull()) {
-      // If the enum has an integer type, it may have been forward declared.
-      // Since we're only looking for a complete type (not a definition), any
-      // visible declaration of it will do.
+    if (OnlyNeedComplete && ED->isFixed()) {
+      // If the enum has a fixed underlying type, and we're only looking for a
+      // complete type (not a definition), any visible declaration of it will
+      // do.
       *Suggested = nullptr;
       for (auto *Redecl : ED->redecls()) {
         if (isVisible(Redecl))