nasm: when generating null targets for WMAKE, add %null
nasm: when generating null targets for WMAKE, add %null

WMAKE wants an explicit %null directive; empty is not ok.

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

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm