don't hardcode OS-depending constant values

The values of the SIG* constants depend on the OS.

Author: xabbuh

Tests/SignalRegistry/SignalMapTest.php

@@ -18,17 +18,21 @@ class SignalMapTest extends TestCase
 {
     /**
      * @requires extension pcntl
-     *
-     * @testWith [2, "SIGINT"]
-     *           [9, "SIGKILL"]
-     *           [15, "SIGTERM"]
-     *           [31, "SIGSYS"]
+     * @dataProvider provideSignals
      */
     public function testSignalExists(int $signal, string $expected)
     {
         $this->assertSame($expected, SignalMap::getSignalName($signal));
     }
 
+    public function provideSignals()
+    {
+        yield [\SIGINT, 'SIGINT'];
+        yield [\SIGKILL, 'SIGKILL'];
+        yield [\SIGTERM, 'SIGTERM'];
+        yield [\SIGSYS, 'SIGSYS'];
+    }
+
     public function testSignalDoesNotExist()
     {
         $this->assertNull(SignalMap::getSignalName(999999));