php.extensions.apcu_bc: Fix runtime loading

Fix an issue brought up in #86463, where the apcu_bc extension isn't
loaded correctly since it produces a .so with a different name than
the extension name. Also, the apcu extension has to be loaded and
loaded prior to loading this extension.

pkgs/top-level/php-packages.nix

@@ -320,11 +320,16 @@ in
 
       sha256 = "0ma00syhk2ps9k9p02jz7rii6x3i2p986il23703zz5npd6y9n20";
 
+      peclDeps = [ php.extensions.apcu ];
+
       buildInputs = [
-        php.extensions.apcu
         pcre'
       ];
 
+      postInstall = ''
+        mv $out/lib/php/extensions/apc.so $out/lib/php/extensions/apcu_bc.so
+      '';
+
       meta.maintainers = lib.teams.php.members;
     };