Fix "make test" with SIGTERM ignored.

If the process that exec'd "make test" had SIGTERM set to SIG_IGN, one
test failed.  That not a clearly-valid use case.  Even so, since all but
one test already survived that scenario, make the last test cope.
https://www.cpantesters.org/report/efbcc1aa-f5f1-11ee-a642-ee3ed50263fb
inspired this.  That smoke tester starting failing when it upgraded from
NetBSD 9.3 to NetBSD 10.0.  I don't know the cause of the failures; this
may or may not fix them.

t/kill_kill.t

@@ -34,16 +34,19 @@ else {
 
 # Test 1
 SCOPE: {
+    my $out;
     my $h = IPC::Run::start(
         [
             $^X,
             '-e',
-            'sleep while 1',
-        ]
+            '$SIG{TERM}="DEFAULT";$|=1;print "running\n";sleep while 1',
+        ],
+        \undef,
+        \$out
     );
-
+    pump $h until $out =~ /running/;
     my $needed = $h->kill_kill;
-    ok( !$needed, 'Did not need kill_kill' );
+    ok( !$needed, 'kill_kill SIGTERM suffices for ordinary command' );
 }
 
 # Test 2
@@ -64,5 +67,5 @@ SKIP: {
     );
     pump $h until $out =~ /running/;
     my $needed = $h->kill_kill( grace => 1 );
-    ok( $needed, 'Did need kill_kill' );
+    ok( $needed, 'kill_kill of SIGINT-ignoring command needs SIGKILL' );
 }