eal/x86: fix pedantic build

eal/x86: fix pedantic build

When enabling pedantic compilation with CONFIG_RTE_LIBRTE_MLX5_DEBUG,
the compiler complains about non standard 128-bit integer type:

include/rte_atomic_64.h:223:3: error:
ISO C does not support ‘__int128’ types [-Werror=pedantic]

It must be marked as an extension of the standard C language
to be accepted in pedantic compilation.

Fixes: 640c5f09ef2c ("eal/x86: add 128-bit atomic compare exchange")
Cc: gage.eads@intel.com
Reported-by: Ferruh Yigit <ferruh.yigit@intel.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Gage Eads <gage.eads@intel.com>
Tested-by: Ferruh Yigit <ferruh.yigit@intel.com>