Add new Mac LIBCPP defines to cpp.hint #2766

Currently, with Mac OS 10, macros _NO_EXCEPT_DEBUG, _LIBCPP_BEGIN_NAMESPACE_STD and _LIBCPP_END_NAMESPACE_STD need to be added to cpp.hint. Let us know if you know of more that need to be added (i.e. #defines that use { or occur at then end of function definitions).

UPDATE:

Should be fixed with 0.21.0-insiders (auto installed if "C_Cpp.updateChannel": "Insiders" is set, or manually installed from the offline vsix). Let us know if you find any problems with it.