libgo: don't use grep -q in mksigtab.sh
libgo: don't use grep -q in mksigtab.sh

Solaris grep does not support the -q option.

Change-Id: Ic080afa161877f0d95a1f8172021c92c69b03746
Reviewed-on: https://go-review.googlesource.com/79239
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend