[Bug preprocessor/79346] -Wundef should not warn for standard macros

[david at westcontrol dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79346

--- Comment #1 from David Brown <david at westcontrol dot com> ---
Some more white-list suggestions for C++ :

__STDCPP_DEFAULT_NEW_ALIGNMENT__
__STDCPP_STRICT_POINTER_SAFETY__
__STDCPP_THREADS__


C++14 also has "Whether __STDC__ is predefined and if so, what its value is,
are implementation-defined".  What makes it a candidate for a white-list.