[clang] [Clang] Do not mark ambiguous specialization invalid. (PR #147275)

[Aaron Ballman via cfe-commits]

================
@@ -4111,7 +4111,10 @@ static ActionResult<CXXRecordDecl *> getPatternForClassTemplateSpecialization(
         if (Ambiguous) {
           // Partial ordering did not produce a clear winner. Complain.
           Inst.Clear();
-          ClassTemplateSpec->setInvalidDecl();
+
+          if (!S.isSFINAEContext())
+            ClassTemplateSpec->setInvalidDecl();
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AaronBallman wrote:

In the absence of a concrete reason to do this, I'd say it's fine to remove the `setInvalidDecl()` entirely as you did originally. Sorry for the noise!

https://github.com/llvm/llvm-project/pull/147275