In the first build the TOOLSDIR does not exit yet which causes CC to default
to the sys.mk version. Once a TOOLSDIR is created during the build though,
this logic was changing CC to ${TOOLSDIR}/usr/bin/cc even though that file
did not exist. Thus CC went from 'cc' to '/usr/bin/cc' which forced a
rebuild of everything while using the same compiler. Check that TOOLSDIR is
not empty to avoid this. If there is actually a TOOLSDIR cc then it will be
used and properly rebuild.
Sponsored by: EMC / Isilon Storage Division
b8aba4fc19