cctool's as needs to be told use to use gnu as, or else we'd need a
dependency cycle between cctools and clang for this case.
In general, this is not a problem because clang uses its own integrated
assembler where possible, and gnu as otherwise.
(cherry picked from commit eb326c9cb7)
Did this when spliting off binutils-wrapper from cc-wrapper in
40e9b2a7e6: I deleted the file instead of
moving it.
(cherry picked from commit 3601a97e3c)