SYSTEM_COMPILER: Ensure there is not a stale compiler in WORLDTMP.

In a scenario of cross-building it is possible that an OBJDIR's WORLDTMP
contains an older compiler in WORLDTMP/usr/bin/cc that is not rebuilt
if SYSTEM_COMPILER logic is triggered. This compiler was still
incorrectly used. Address this by removing WORLDTMP/usr/bin/cc and all
of the hardlinked files associated with it. Also do this for c++ for
GCC builds.

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