Move xpg4 'id' handling into test-exec.sh.

Handle replacement of 'id' the same way as we do other Portable specific
replacements in test-exec.sh.  This brings percent.sh back into sync
with upstream.

regress/percent.sh

@@ -3,11 +3,6 @@
 
 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.`

regress/test-exec.sh

@@ -392,6 +392,7 @@ have_prog()
 jot() {
 	awk "BEGIN { for (i = $2; i < $2 + $1; i++) { printf \"%d\n\", i } exit }"
 }
+
 if [ ! -x "`which rev`" ]; then
 rev()
 {
@@ -399,6 +400,13 @@ rev()
 }
 fi
 
+if [ -x "/usr/xpg4/bin/id" ]; then
+id()
+{
+	/usr/xpg4/bin/id
+}
+fi
+
 # Check whether preprocessor symbols are defined in config.h.
 config_defined ()
 {