bug #42091 [Console] Run commands when implements SignalableCommandInterface without pcntl and they have'nt signals (PaolaRuby)

This PR was squashed before being merged into the 5.2 branch.

Discussion
----------

[Console] Run commands when implements SignalableCommandInterface without pcntl and they have'nt signals

| Q             | A
| ------------- | ---
| Branch?       | 5.2
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix [#42076](symfony/symfony#42076)
| License       | MIT

When a command extends a class wich implements SignalableCommandInterface but the command has empty signals to dispatch, it still can be executed, It can be useful when the extension is not available and the command is necessary.
Also, it can be used like a workaround for support other environments, for example windows servers, they don't have pcntl extension

Commits
-------

ad63d0b553 [Console] Run commands when implements SignalableCommandInterface without pcntl and they have'nt signals

Author: nicolas-grekas

Application.php

@@ -940,7 +940,7 @@ protected function doRunCommand(Command $command, InputInterface $input, OutputI
             }
         }
 
-        if ($command instanceof SignalableCommandInterface) {
+        if ($command instanceof SignalableCommandInterface && ($this->signalsToDispatchEvent || $command->getSubscribedSignals())) {
             if (!$this->signalRegistry) {
                 throw new RuntimeException('Unable to subscribe to signal events. Make sure that the `pcntl` extension is installed and that "pcntl_*" functions are not disabled by your php.ini\'s "disable_functions" directive.');
             }

Tests/ApplicationTest.php

@@ -36,6 +36,7 @@
 use Symfony\Component\Console\Output\Output;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Output\StreamOutput;
+use Symfony\Component\Console\SignalRegistry\SignalRegistry;
 use Symfony\Component\Console\Tester\ApplicationTester;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\EventDispatcher\EventDispatcher;
@@ -1861,6 +1862,18 @@ public function testSignal()
         $this->assertTrue($command->signaled);
         $this->assertTrue($dispatcherCalled);
     }
+
+    public function testSignalableCommandInterfaceWithoutSignals()
+    {
+        $command = new SignableCommand();
+
+        $dispatcher = new EventDispatcher();
+        $application = new Application();
+        $application->setAutoExit(false);
+        $application->setDispatcher($dispatcher);
+        $application->add($command);
+        $this->assertSame(0, $application->run(new ArrayInput(['signal'])));
+    }
 }
 
 class CustomApplication extends Application
@@ -1928,7 +1941,7 @@ class SignableCommand extends Command implements SignalableCommandInterface
 
     public function getSubscribedSignals(): array
     {
-        return [\SIGALRM];
+        return SignalRegistry::isSupported() ? [\SIGALRM] : [];
     }
 
     public function handleSignal(int $signal): void