Use /usr/bin/xp4g/id if necessary.

Solaris' native "id" doesn't support the options we use but the one
in /usr/bin/xp4g does, so use that instead.

regress/percent.sh

@@ -3,6 +3,11 @@
 
 tid="percent expansions"
 
+if [ -x "/usr/xpg4/bin/id" ]; then
+	PATH=/usr/xpg4/bin:$PATH
+	export PATH
+fi
+
 USER=`id -u -n`
 USERID=`id -u`
 HOST=`hostname | cut -f1 -d.`