t/loc_tools.pl: Check for unsupported locales

This commit causes us not to view unsupported locales as legitimate for
testing.  Core dumps occurred on some platforms without this.

It looks for a diagnostic that the next commit in this series will
generate.

t/loc_tools.pl

@@ -148,11 +148,13 @@ ($$$$)
 
     my $badutf8 = 0;
     my $plays_well = 1;
+    my $unsupported = 0;
 
     use warnings 'locale';
 
     local $SIG{__WARN__} = sub {
         $badutf8 = 1 if grep { /Malformed UTF-8/ } @_;
+        $unsupported = 1 if grep { /Locale .* is unsupported/i } @_;
         $plays_well = 0 if grep {
                     /Locale .* may not work well(?#
                    )|The Perl program will use the expected meanings/i
@@ -187,6 +189,8 @@ ($$$$)
             return;
         }
 
+        return if $unsupported;
+
         # Commas in locale names are bad in Windows, and there is a bug in
         # some versions where setlocale() turns a legal input locale name into
         # an illegal return value, which it can't later parse.