tests/variables.sh: Fix locale tests (#247)

src/cmd/ksh93/tests/variables.sh: LC_* error tests:
- Since operating systems validate locale strings differently,
  try a few different bad locale strings to find one that makes
  setlocale(2) fail, fixing test failures on OpenBSD and Debian.
- Restore warning removed in aed5c6d7, issuing it if none of the
  bad locale strings produce a diagnostic.
- Reenable test for diagnostic message disabled in aed5c6d7.

Co-authored-by: Martijn Dekker <martijn@inlv.org>

src/cmd/ksh93/tests/variables.sh

@@ -736,15 +736,22 @@ unset r v x
 )
 Errors=$?  # ensure error count survives subshell
 (
-	errmsg=$({ LANG=bad_LOCALE; } 2>&1)
+	# $x must be an unknown locale.
-	x=x
+	for x in x x.b@d xx_XX xx_XX.b@d
+	do	errmsg=$({ LANG=$x; } 2>&1)
+		[[ -n $errmsg ]] && break
+	done
+	if	[[ -z $errmsg ]]
+	then	warning "C library does not seem to verify locales: skipping LC_* tests"
+		exit $Errors
+	fi
+
 	for v in LC_ALL LC_CTYPE LC_MESSAGES LC_COLLATE LC_NUMERIC
 	do	nameref r=$v
 		unset $v
 		[[ $r ]] && err_exit "unset $v failed -- expected '', got '$r'"
-		# Test disabled: some system libraries do not verify the locale, so no diagnostic is printed.
+		d=$($SHELL -c "$v=$x" 2>&1)
-		#d=$($SHELL -c "$v=$x" 2>&1)
+		[[ $d ]] || err_exit "$v=$x failed -- expected locale diagnostic"
-		#[[ $d ]] || err_exit "$v=$x failed -- expected locale diagnostic"
 		{ g=$( r=$x; print -- $r ); } 2>/dev/null
 		[[ $g == '' ]] || err_exit "$v=$x failed -- expected '', got '$g'"
 		{ g=$( r=C; r=$x; print -- $r ); } 2>/dev/null