[Completion] Check for callback rather than result of ResolveMacroRequest

When doing solver-based completion, the request
will fail, avoid falling back to a regular call
expression in that case; we only care about
whether we got the callback.

rdar://129024996

Author: hamishknight

lib/IDE/CodeCompletion.cpp

@@ -1431,14 +1431,14 @@ void CodeCompletionCallbacksImpl::typeCheckWithLookup(
     /// decl it could be attached to. Type check it standalone.
 
     // First try to check it as an attached macro.
-    auto resolvedMacro = evaluateOrDefault(
+    (void)evaluateOrDefault(
         CurDeclContext->getASTContext().evaluator,
         ResolveMacroRequest{AttrWithCompletion, CurDeclContext},
         ConcreteDeclRef());
 
     // If that fails, type check as a call to the attribute's type. This is
     // how, e.g., property wrappers are modelled.
-    if (!resolvedMacro) {
+    if (!Lookup.gotCallback()) {
       ASTNode Call = CallExpr::create(
           CurDeclContext->getASTContext(), AttrWithCompletion->getTypeExpr(),
           AttrWithCompletion->getArgs(), /*implicit=*/true);