AST: AbstractGenericSignatureRequest and InferredGenericSignatureRequest return the HadAnyError bit

For now I'm going to use this in -verify-generic-signatures, but
it could be useful in other places too.

lib/AST/GenericSignature.cpp

@@ -1749,5 +1749,5 @@ swift::buildGenericSignature(ASTContext &ctx,
         baseSignature.getPointer(),
         addedParameters,
         addedRequirements},
-      GenericSignature());
+      GenericSignatureWithError()).getPointer();
 }