If you want to track MirOS-current, be aware that /usr/libexec/cpp changed and /usr/bin/cpp is gone; you must compile and install a new cpp first, then stuff like rpcgen(1) and lint(1), then remove the /usr/bin/cpp script.
Furthermore, the gcc-provided shared libraries and items have moved from /usr/lib to /usr/lib/gcc/OStriplet/3.4.6 which you should add to shlib_dirs in /etc/rc.conf.local until you have rebuilt everything (base system and ports). Both mgcc and llvm-gcc add appropriate DT_RPATH to programmes and shared objects compiled with them and use their own crtstuff; mircvs://src/lib/csu/ now provides crtstuff for use with pcc(!) instead.
Expect a new i386 snapshot some time soon; sparc snapshots are planned more for the long term but could be compiled on request (ETA one week).