Python will record the values of CC, CXX, AR, and READELF (and other
configure options) used during compilation. pip will use these programs
when asked to compile extension modules on the target device.

* If ccache is used during build, CC and CXX will be ccache_cc and
  ccache_cxx, respectively, which are not available on-device (#11912).

* If an external toolchain is used during build, the values of these
  variables will contain the external toolchain prefix, which may not be
  available on target.

* If the normal toolchain is used during build, AR and READELF will
  contain the toolchain prefix, but the names of ar and readelf
  on-device do not contain the prefix; they are named "ar" and
  "readelf".

This changes the values of these variables in Python's files to match
the names available on-device, and without any toolchain prefix.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>