libepoxy: disable glx on darwin by default

Originally enabled in

950261bb9a ('darwin: fix gtk+3 dependencies')

since then many dependencies may have been changed to rely on Cocoa
only. Let's try disabling it by default to avoid the mesa dependency
on darwin, we can always enable on a case-by-case basis for apps that
really use X11.

pkgs/development/libraries/gtk/3.x.nix

@@ -104,7 +104,7 @@ stdenv.mkDerivation rec {
 
   buildInputs = [
     libxkbcommon
-    libepoxy
+    (libepoxy.override { inherit x11Support; })
     isocodes
   ] ++ lib.optionals stdenv.isDarwin [
     AppKit

pkgs/development/libraries/gtk/4.x.nix

@@ -95,7 +95,7 @@ stdenv.mkDerivation rec {
     libpng
     libtiff
     libjpeg
-    libepoxy
+    (libepoxy.override { inherit x11Support; })
     isocodes
   ] ++ lib.optionals vulkanSupport [
     vulkan-headers

pkgs/development/libraries/libepoxy/default.nix

@@ -10,6 +10,7 @@
 , libX11
 , Carbon
 , OpenGL
+, x11Support ? !stdenv.isDarwin
 }:
 
 let
@@ -40,7 +41,7 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ meson ninja pkg-config utilmacros python3 ];
 
-  buildInputs = [
+  buildInputs = lib.optionals x11Support [
     libGL
     libX11
   ] ++ lib.optionals stdenv.isDarwin [
@@ -50,10 +51,10 @@ stdenv.mkDerivation rec {
 
   mesonFlags = [
     "-Dtests=${if doCheck then "true" else "false"}"
-  ]
-  ++ optional stdenv.isDarwin "-Dglx=yes";
+    "-Dglx=${if x11Support then "yes" else "no"}"
+  ];
 
-  NIX_CFLAGS_COMPILE = ''-DLIBGL_PATH="${getLib libGL}/lib"'';
+  NIX_CFLAGS_COMPILE = lib.optionalString x11Support ''-DLIBGL_PATH="${getLib libGL}/lib"'';
 
   # cgl_epoxy_api fails in darwin sandbox and on Hydra (because it's headless?)
   preCheck = lib.optionalString stdenv.isDarwin ''