srb2: patch missing libGLU dependency

Fixes the following error:

hwOpen of libGLU.so.1: Failed loading libGLU.so.1: libGLU.so.1: cannot
open shared object file: No such file or directory

ERROR: Could not load GLU Library: libGLU.so.1

pkgs/by-name/sr/srb2/package.nix

@@ -7,6 +7,7 @@
 , nasm
 , libopenmpt
 , game-music-emu
+, libGLU
 , libpng
 , SDL2
 , SDL2_mixer
@@ -80,6 +81,11 @@ stdenv.mkDerivation (finalAttrs: {
     ./thirdparty.patch
   ];
 
+  postPatch = ''
+    substituteInPlace ./src/sdl/ogl_sdl.c \
+      --replace libGLU.so.1 ${libGLU}/lib/libGLU.so.1
+  '';
+
   desktopItems = [
     (makeDesktopItem rec {
       name = "Sonic Robo Blast 2";