$NetBSD: patch-scripts_snapstamp,v 1.2 2020/03/18 13:49:30 gdt Exp $

Remediate bashisms.

Sent upstream by email 20200317.

--- scripts/snapstamp.orig	2019-05-25 19:15:55.000000000 +0000
+++ scripts/snapstamp
@@ -17,4 +17,4 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-[[ -n $STP_BUILD_SNAPSHOT && -d .git ]] && printf '%s%(%Y-%m-%dT%H-%M)T-%s' - -1 $(git describe --dirty --always --first-parent --exclude '*')
+[ -n "$STP_BUILD_SNAPSHOT" && -d .git ] && printf '%s%(%Y-%m-%dT%H-%M)T-%s' - -1 $(git describe --dirty --always --first-parent --exclude '*')