lib9: format %#04x, 0 as 0x0000 not 000000.
lib9: format %#04x, 0 as 0x0000 not 000000.

This matches Go's fmt.Printf instead of ANSI C's dumb rules.
It makes the -S output from C liblink match Go's liblink.

LGTM=minux
R=minux
CC=golang-codereviews
https://codereview.appspot.com/112600043

tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go