performtest: use -u with diff
performtest: use -u with diff

Unified diffs are the only sane option.  When calling diff, pass the
-u option.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

projedi/nasm,turingstudio/nasm,techkey/nasm,turingstudio/nasm,letolabs/nasm,Distrotech/nasm,projedi/nasm,letolabs/nasm,techkey/nasm,techkey/nasm,Distrotech/nasm,techkey/nasm,turingstudio/nasm,Distrotech/nasm,techkey/nasm,projedi/nasm,projedi/nasm,projedi/nasm,letolabs/nasm,Distrotech/nasm,turingstudio/nasm