base: Avoid circular references to our own scripts

We'd like to intercept git calls but we don't want circular references
and HOSTTOOLS currently sets them up. Tweak to avoid them.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 52c37e13)
Signed-off-by: Steve Sakoman <steve@sakoman.com>