Added support for IPv6 requirement

I decided to add two additional PHP interpreter packages instead of an additional extension key. IPv6 support is part of PHP core (if enabled) and is not part of any optional extension.

src/Composer/Repository/PlatformRepository.php

@@ -77,14 +77,29 @@ class PlatformRepository extends ArrayRepository
             $version = $versionParser->normalize($prettyVersion);
         }
 
+        // The AF_INET6 constant is only defined if ext-sockets is available but IPv6 support might still be available.
+        $ipv6Support = defined('AF_INET6') || @inet_pton('::') !== false;
+
         $php = new CompletePackage('php', $version, $prettyVersion);
         $php->setDescription('The PHP interpreter');
         $this->addPackage($php);
 
+        if ($ipv6Support) {
+            $phpIpv6 = new CompletePackage('php-ipv6', $version, $prettyVersion);
+            $phpIpv6->setDescription('The PHP interpreter with IPv6 support');
+            $this->addPackage($phpIpv6);
+        }
+
         if (PHP_INT_SIZE === 8) {
             $php64 = new CompletePackage('php-64bit', $version, $prettyVersion);
             $php64->setDescription('The PHP interpreter, 64bit');
             $this->addPackage($php64);
+
+            if ($ipv6Support) {
+                $php64Ipv6 = new CompletePackage('php-64bit-ipv6', $version, $prettyVersion);
+                $php64Ipv6->setDescription('The PHP interpreter with IPV6 support, 64bit');
+                $this->addPackage($php64Ipv6);
+            }
         }
 
         $loadedExtensions = get_loaded_extensions();