meterbridge: fix build

commit 7aeac03 (PR #386495) dropped libX11 and libGLU from propagatedBuildInputs in SDL_compat, and #389106 pointed SDL to SDL_compat, which broke this build

Hydra fail: https://hydra.nixos.org/build/292743363

pkgs/by-name/me/meterbridge/package.nix

···
   stdenv,
   fetchurl,
   pkg-config,
+  libGL,
   SDL,
   SDL_image,
   libjack2,
···
 
   nativeBuildInputs = [ pkg-config ];
   buildInputs = [
+    libGL
     SDL
     SDL_image
     libjack2