Followup to 48e26c3afe, and discussions in !134771 about keeping
'C-style' and 'C++ template type-safe style' implementations of our
guardedalloc separated. And it makes `MEM_freeN<T>` code simpler.
Also skip type-checking in `MEM_freeN<T>` only with MSVC, as clang-cl on
windows-arm64 does work fine with DNA structs using
`DNA_DEFINE_CXX_METHODS`.
Pull Request: https://projects.blender.org/blender/blender/pulls/134861
318ae49f1e