Proven recipe pattern for gnulib cross-compilation on Redox:
1. fix_types.h with guarded typedefs for ALL sys/types.h types
2. Strip raw typedefs from GL_CFLAG_GNULIB_WARNINGS after configure
3. Set cache vars for functions gnulib can't detect
Remaining: __fseterr/__freadahead stubs for linker (need relibc-level
or recipe-level .o injection)