* gnatboot can't be used as cross compiler, so we should prevent this at
eval time.
* Explicitly checking hostPlatform is also a lot nicer. Keeping system
since gnatboot seems to be statically linked so gnu/musl which is also
tracked in config isn't important.
Some things don't work:
- The ghdl expression (it still needs the gcc 4.3.4 src, ...)
- The gnat wrappers need to be more generic - now they work only for the
given gnatboot (taken from gentoo) and gnats installed to their $out
store path.
- Using the cloogppl and ppl. We will need our own gnatboot built with c++
libraries for that.
svn path=/nixpkgs/branches/stdenv-updates/; revision=19060
