[CS] Prevent callAsFunction from being used on AnyObject

Previously this hit an assertion in CSApply.
While we could technically make it work, it's
probably best not to allow it.

Resolves SR-11829.

Author: hamishknight

lib/AST/Type.cpp

@@ -1481,6 +1481,10 @@ bool TypeBase::satisfiesClassConstraint() {
 }
 
 bool TypeBase::isCallableNominalType(DeclContext *dc) {
+  // Don't allow callAsFunction to be used with dynamic lookup.
+  if (isAnyObject())
+    return false;
+
   // If the type cannot have members, we're done.
   if (!mayHaveMembers())
     return false;

test/Constraints/dynamic_lookup.swift

@@ -398,3 +398,13 @@ class HasMethodWithDefault {
 func testAnyObjectWithDefault(_ x: AnyObject) {
   x.hasDefaultParam()
 }
+
+// SR-11829: Don't perform dynamic lookup for callAsFunction.
+class ClassWithObjcCallAsFunction {
+  @objc func callAsFunction() {}
+}
+
+func testCallAsFunctionAnyObject(_ x: AnyObject) {
+  x() // expected-error {{cannot call value of non-function type 'AnyObject'}}
+  x.callAsFunction() // Okay.
+}