gperf: Add a patch to work around reproducibility issues

Add a patch to avoid writing the full pathname to gperf into source
files which leads to reproducibility issues.

This fixes issues with systemd reproducibility in particular.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit dea3c7ee)
Signed-off-by: Steve Sakoman <steve@sakoman.com>