mesa: automake: ensure that git_sha1.h.tmp has the right attributes
... when copied from git_sha1.h.
As the latter file can we lacking the write attribute, one should set it
explicitly. Otherwise we'll get a warning/failure at cleanup stage.
Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by:
Emil Velikov <emil.velikov@collabora.com>