gc: fix import width bug

src/cmd/5g/cgen.c

src/cmd/6g/cgen.c

src/cmd/8g/cgen.c

src/cmd/gc/dcl.c

src/cmd/gc/walk.c

test/fixedbugs/bug335.dir/a.go

test/fixedbugs/bug335.dir/b.go

test/fixedbugs/bug335.go