Adjust USES to attempt to get past the following build failure on
GCC-based systems:

cc1: error: unrecognized command line option "-std=gnu11"

However, this merely uncovers another error: the use of hardcoded x86
assembler.

The website is silent on the issue of whether it has ever been tested
on !x86.

Therefore, mark it ONLY_FOR x86.

Approved by: portmgr (tier-2 blanket)