shtests: make aliases work again for shcomp tests (re: aed5c6d7)

Moving the 'err_exit' and 'warning' alias definitions in the
regression tests to one _common file introduced a bug: they are no
longer expanded at compile time when the tests are run with shcomp,
resulting in a 'command not found' (at best) on trying to execute
one. shcomp requires that the alias definitions need to be present
in the file itself. But that means maintaining 50-odd copies again.
I'd rather add a hack to shtests to avoid this.

src/cmd/ksh93/tests/shtests:
- Before running a test with shcomp, physically concatenate _common
  and the test script together into a temporary file, minus the '.'
  command that includes _common, and compile that with shcomp.

src/cmd/ksh93/tests/shtests

@@ -8,7 +8,7 @@ valgrindflags='--xml=yes --log-file=/dev/null --track-origins=yes --read-var-inf
 
 USAGE=$'
 [-s8?
-@(#)$Id: shtests (ksh 93u+m) 2021-03-06 $
+@(#)$Id: shtests (ksh 93u+m) 2021-03-23 $
 ]
 [-author?David Korn <dgk@research.att.com>]
 [-author?Glenn Fowler <gsf@research.att.com>]
@@ -405,8 +405,13 @@ do	[[ $i == *.sh ]] || i+='.sh'
 		echo test $o begins ${time:+"at $(date +%Y-%m-%d+%H:%M:%S)"}
 		tmp_s=$tmp/$u.shcomp
 		mkdir -m700 "$tmp_s" || exit
+		# must incorporate _common in script itself so the aliases are expanded at compile time
+		sed '/^\. .*\/_common/ {
+			r _common
+			d
+		}' < $i > $c.orig
 		cd "$tmp_s" || exit
-		if	$SHCOMP "$OLDPWD/$i" > $c
+		if	"$SHCOMP" "$c.orig" > $c
 		then	if	tmp=$tmp_s $valgrind $SHELL $trace $c
 			then	echo test $o passed ${time:+"at $(date +%Y-%m-%d+%H:%M:%S)"} "[ $t $T 0 errors ]"
 			else	e=$?