Log Message:
bl3ify the gcc3-* packages.  Also provide buildlink[23].mk files for use
by bsd.compiler.mk.  Note that in the buildlink3.mk files, the dependency
is always added regardless of the BUILDLINK_DEPTH.  This is because these
buildlink3.mk files may be included by bsd.prefs.mk, which is often
included other buildlink3.mk files, and we need to ensure that regardless
of the depth, we are using the correct compiler.