- add fixes from upstream (bumping portrevision)
- permit overriding USE_GCC from environment (but note that GCC is
required due to GCC extensions that are unsupported by clang)
- actually pass CC and CXX as themselves, and HOSTCC/HOSTCXX through
MAKE_ARGS, so that it actually gets effective
- add install conflict with busybox-unstable
busybox-unstable:
- new port, based on the fixed busybox, for the unstable 1.21 branch,
with install conflict with busybox-[1-9]*
