[Type refinement context] Don't recurse into macro expansions.

Macro expansion buffers will have their type refinement contexts built
lazily, associated with the source file for the macro expansion
buffer. By not recursing into macro expansions, we break false
reference cycles among different files.

Fixes rdar://107394143

Author: DougGregor

lib/Sema/TypeCheckAvailability.cpp

@@ -473,7 +473,7 @@ class TypeRefinementContextBuilder : private ASTWalker {
 
 private:
   MacroWalking getMacroWalkingBehavior() const override {
-    return MacroWalking::ArgumentsAndExpansion;
+    return MacroWalking::Arguments;
   }
 
   PreWalkAction walkToDeclPre(Decl *D) override {

test/Macros/Inputs/top_level_freestanding_other.swift

@@ -1,2 +1 @@
-// FIXME(rdar://107394143): Circular reference bug
-// #anonymousTypes { "hello2" }
+#anonymousTypes { "hello2" }