Fix f128 NaN check on big-endian hosts
Fix f128 NaN check on big-endian hosts

On big-endian hosts, zig_f128_isNaN() takes the high and low halves
from the wrong element, resulting in buggy NaN detection behavior.
This fixes it.

raulgrell/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig