Fix farith and farithp instructions for GAS mode (e.g. fsubr).

The easiest way to fix these was to adjust the GAP input file to have NASM
and GAS versions of these instructions.

Tests added to check both NASM and GAS (farith.asm and gas-farithr.asm
respectively).

svn path=/trunk/yasm/; revision=1579
9 files changed