mujoco: add libGL to propagatedBuildInputs

This is needed when consuming MuJoCo with `find_package(mujoco)` as it
explicitely checks for `find_dependency(OpenGL)` in its
`mujocoConfig.cmake` file

pkgs/by-name/mu/mujoco/package.nix

@@ -6,6 +6,7 @@
   gitMinimal,
   fetchFromGitLab,
   glfw,
+  libGL,
   glm,
   spdlog,
   cereal,
@@ -109,6 +110,11 @@ stdenv.mkDerivation (finalAttrs: {
     glfw
   ];
 
+  propagatedBuildInputs = [
+    # consuming MuJoCo through cmake find_package requires libGL
+    libGL
+  ];
+
   cmakeFlags = [
     (lib.cmakeBool "MUJOCO_SIMULATE_USE_SYSTEM_GLFW" true)
     (lib.cmakeBool "MUJOCO_SAMPLES_USE_SYSTEM_GLFW" true)