BUILD_CC may reference something like ccache and expect this to come from
ccache-native, we at least have some selftests which assume this. Modify the
code to use PATH when runnig BUILD_CC to ensure the tests continue to work
as expected.
(From OE-Core rev: f3e753372baac43d0921186340cf260df056de20)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>