uhexen2: fix the build against SDL_compat

Without the change build fails due to missing libraries as
https://hydra.nixos.org/build/294936344:

../h2shared/glheader.h:40:10: fatal error: GL/gl.h: No such file or directory
40 | #include <GL/gl.h>
| ^~~~~~~~~

pkgs/by-name/uh/uhexen2/package.nix

···
   fetchgit,
   SDL,
   stdenv,
+  alsa-lib,
+  libGL,
   libogg,
   libvorbis,
   libmad,
···
 
   buildInputs = [
     SDL
+    alsa-lib
+    libGL
     libogg
     libvorbis
     libmad