Makefile: disallow data races on gcc-10 as well

gcc-10 will rename --param=allow-store-data-races=0
to -fno-allow-store-data-races.

The flag change happened at https://gcc.gnu.org/PR92046.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>