apache-httpd: add phpPackage option

nixos/modules/services/web-servers/apache-httpd/default.nix

···
 
   httpdConf = mainCfg.configFile;
 
-  php = pkgs.php.override { apacheHttpd = httpd.dev; /* otherwise it only gets .out */ };
+  php = mainCfg.phpPackage.override { apacheHttpd = httpd.dev; /* otherwise it only gets .out */ };
+
+  phpMajorVersion = head (splitString "." php.version);
 
   getPort = cfg: if cfg.port != 0 then cfg.port else if cfg.enableSSL then 443 else 80;
 
···
           concatMap (svc: svc.extraModulesPre) allSubservices
           ++ map (name: {inherit name; path = "${httpd}/modules/mod_${name}.so";}) apacheModules
           ++ optional mainCfg.enableMellon { name = "auth_mellon"; path = "${pkgs.apacheHttpdPackages.mod_auth_mellon}/modules/mod_auth_mellon.so"; }
-          ++ optional enablePHP { name = "php5"; path = "${php}/modules/libphp5.so"; }
+          ++ optional enablePHP { name = "php${phpMajorVersion}"; path = "${php}/modules/libphp${phpMajorVersion}.so"; }
           ++ concatMap (svc: svc.extraModules) allSubservices
           ++ extraForeignModules;
       in concatMapStrings load allModules
···
         type = types.bool;
         default = false;
         description = "Whether to enable the PHP module.";
+      };
+
+      phpPackage = mkOption {
+        type = types.package;
+        default = pkgs.php;
+        defaultText = "pkgs.php";
+        description = ''
+          Overridable attribute of the PHP package to use.
+        '';
       };
 
       phpOptions = mkOption {