util/xcompile/xcompile: Remove -Wno-unused-but-set-variable from CFLAGS

Do not disable warnings about unused but set variables to further
improve the code quality.

Change-Id: I25fa29ac42c9d09596d03f11fb01f31635a62a11
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: https://review.coreboot.org/3981
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)
1 file changed