Blender Git Loki

CMake: Tweaks to removal of strict flags

Silences the following strict flags from external libraries:

- -Wclass-memaccess
- -Wswitch
- -Wtype-limits
- -Wint-in-bool-context

Needed to tweak macro a bit, since the old logic was wrong:
we can not use CXX flags for C compiler, need way more strict
separation between what goes where.