check-uapi: honor ${CROSS_COMPILE} setting

check-uapi: honor ${CROSS_COMPILE} setting

When ${CROSS_COMPILE} is set, but ${CC} is not set, the logic in
check-uapi.sh is different from the top-level Makefile, which defaults
to using the cross gcc. This leads to using the native gcc instead of the
cross version, resulting in unexpected false-positive and false-negative
output.

Use the same logic here that we use in Kbuild for consistency.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20260306163309.2015837-3-arnd@kernel.org
Signed-off-by: Nicolas Schier <nsc@kernel.org>