We want platform triple prefixes and suffixes on derivation names to
be used consistently. The ideom this commit strives for is
- suffix means build != host, i.e. cross *built* packages. This is
already done.
- prefix means build != target, i.e. cross tools. This matches the
tradition of such binaries themselves being prefixed to disambiguate.]
Binutils and cctools, as build tools, now use the latter
7018dfb9f4