The cross-compiler's GCC built-in stddef.h is blocked by relibc's
_STDDEF_H guard, causing size_t/off_t/ptrdiff_t to be undefined.
Add fix_types.h with guarded typedefs and force-include via CPPFLAGS.
Also: comprehensive upstream relibc comparison for systematic import.
Remaining: redoxer env overrides CC, injecting broken stdint typedefs
from its toolchain. This needs a redoxer-level fix to clean the
injected flags before passing to build commands.
vasilito