We don't enable this on any other architecture.
-pedantic doesn't give us any more beneficial wanrings, only warns
about language extensions that are implemented by both GCC and Clang
anyway.
Since those are the only compilers we are targeting, we can just make
use of them to make our lives easier.
Adds a separate board for native64 instead of the `NATIVE_64BIT` workaround.
The files in `boards/native64` are more or less dummy files and just include
the `boards/native` logic (similar to `openlabs-kw41z-mini-256kib`).
The main logic for native is in `makefiles/arch/native.inc.mk`, `cpu/native`
and `boards/native`.
The remaining changes concern the build system, and change native board checks
to native CPU checks to cover both boards.
