xxhash: fix build with gcc 12

It fails to compile xxhash when '-Og' is set in CFLAGS via such as set
DEBUG_BUILD = '1' in local.conf. Check and disable inline when '-Og'
exists.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>