[libclang] Make clang_getCursor able to handle locations that point inside macro arguments.

e.g. for:

\define INVOKE(METHOD, CLASS) [CLASS METHOD]

void test2() {
  INVOKE(meth, MyClass);
}

Pointing at 'meth' will give a CXCursor_ObjCMessageExpr and pointing at 'MyClass'
will give a CXCursor_ObjCClassRef.

llvm-svn: 137796