MS ABI: Delay default constructor closure checking until the outermost class scope ends

Previously, we would error out on this code because the default argument
wasn't parsed until the end of Outer:

  struct __declspec(dllexport) Outer {
    struct __declspec(dllexport) Inner {
      Inner(void *p = 0);
    };
  };

Now we do the checking on the closing brace of Outer instead of Inner.

llvm-svn: 232519