php.buildEnv: Provide the unwrapped php package in php.unwrapped

This is useful if you need to access the dev output of the unwrapped
derivation.

pkgs/development/interpreters/php/default.nix

@@ -119,6 +119,7 @@ let
                   buildEnv = mkBuildEnv allArgs allExtensionFunctions;
                   withExtensions = mkWithExtensions allArgs allExtensionFunctions;
                   phpIni = "${phpWithExtensions}/lib/php.ini";
+                  unwrapped = php;
                   inherit (php-packages) packages extensions;
                 };
                 paths = [ php ];