[Parser][ObjC] Make sure c++11 in-class initialization is done when the

[Parser][ObjC] Make sure c++11 in-class initialization is done when the
constructor's definition is in an implementation block.

Without this commit, ptr doesn't get initialized to null in the
following code:

struct S {
  S();
  void *ptr = nullptr;
};

@implementation I
  S::S() {}
@end

rdar://problem/25693624

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@266645 91177308-0d34-0410-b5e6-96231b3b80d8