{libGL,libGLU}: use the OpenGL framework on Darwin

This reduces the reverse closure of Mesa on Darwin considerably. As
a result, we can also drop the Mesa stubs package entirely, as its
output on Linux is functionally identical to libglvnd.

It should no longer be necessary for packages to switch between libGL
and darwin.apple_sdk.frameworks.OpenGL depending on the platform.

A cross‐platform libGLX alias is added for packages that specifically
need it (mostly old X11 applications that barely know what a macOS is).

Co-authored-by: K900 <me@0upti.me>

pkgs/top-level/all-packages.nix

@@ -23210,16 +23210,41 @@ with pkgs;
 
   ## libGL/libGLU/Mesa stuff
 
-  # Default libGL implementation, should provide headers and
-  # libGL.so/libEGL.so/... to link agains them. Android NDK provides
-  # an OpenGL implementation, we can just use that.
-  libGL = if stdenv.hostPlatform.useAndroidPrebuilt then stdenv
-          else callPackage ../development/libraries/mesa/stubs.nix {
-            inherit (darwin.apple_sdk.frameworks) OpenGL;
-          };
+  # Default libGL implementation.
+  #
+  # Android NDK provides an OpenGL implementation, we can just use that.
+  #
+  # On macOS, we use the OpenGL framework. Packages that still need GLX
+  # specifically can pull in libGLX instead. If you have a package that
+  # should work without X11 but it can’t find the library, it may help
+  # to add the path to `NIX_CFLAGS_COMPILE`:
+  #
+  #     -L${libGL}/Library/Frameworks/OpenGL.framework/Versions/Current/Libraries
+  #
+  # If you still can’t get it working, please don’t hesitate to ping
+  # @NixOS/darwin-maintainers to ask an expert to take a look.
+  libGL =
+    if stdenv.hostPlatform.useAndroidPrebuilt then
+      stdenv
+    else if stdenv.hostPlatform.isDarwin then
+      darwin.apple_sdk.frameworks.OpenGL
+    else
+      libglvnd;
 
-  # Default libGLU
-  libGLU = mesa_glu;
+  # On macOS, we use the OpenGL framework. Packages that use libGLX on
+  # macOS may need to depend on mesa_glu directly if this doesn’t work.
+  libGLU =
+    if stdenv.hostPlatform.isDarwin then
+      darwin.apple_sdk.frameworks.OpenGL
+    else
+      mesa_glu;
+
+  # libglvnd does not work (yet?) on macOS.
+  libGLX =
+    if stdenv.hostPlatform.isDarwin then
+      mesa
+    else
+      libglvnd;
 
   mesa = if stdenv.isDarwin
     then darwin.apple_sdk_11_0.callPackage ../development/libraries/mesa/darwin.nix {