FreeBSD's probably not the best example you could have picked; it can already build on a non-GCC compiler, Clang (for x86 and x64, at least): http://wiki.freebs

FreeBSD's probably not the best example you could have picked; it can already build on a non-GCC compiler, Clang (for x86 and x64, at least): http://wiki.freebsd.org/BuildingFreeBSDWithClang http://wiki.freebsd.org/BuildingFreeBSDWithClang. And the last time I looked, it was more of "Clang not being complete" then anything else to hold up DragonFly BSD from compiling. Not sure about the state of OpenBSD or NetBSD with Clang, though.