Wiki about GNUstep and friends.

===== TODO =====
  * Configure GNUstep-Make to use the non-fragile ABI.  CC and CXX should be clang and clang++, respectively
  * Remove dependency on GCC, use system clang (or clang port if not available) with libobjc2
  * Find gnustep ports that don't work with the non-fragile ABI and either:
    - Fix them, or
    - Import newer versions (e.g. from GAP)
  * Clean out ancient ports (e.g. old versions of Étoilé frameworks and earlier)