mesa: fix darwin build

pkgs/development/libraries/mesa/default.nix

@@ -4,7 +4,7 @@
 , expat, libdrm, xorg, wayland, wayland-protocols, openssl
 , llvmPackages, libffi, libomxil-bellagio, libva-minimal
 , libelf, libvdpau
-, libglvnd
+, libglvnd, libunwind
 , galliumDrivers ? ["auto"]
 , driDrivers ? ["auto"]
 , vulkanDrivers ? ["auto"]
@@ -127,6 +127,7 @@ self = stdenv.mkDerivation {
     libpthreadstubs openssl /*or another sha1 provider*/
   ] ++ lib.optionals (elem "wayland" eglPlatforms) [ wayland wayland-protocols ]
     ++ lib.optionals stdenv.isLinux [ libomxil-bellagio libva-minimal ]
+    ++ lib.optionals stdenv.isDarwin [ libunwind ]
     ++ lib.optional withValgrind valgrind-light;
 
   depsBuildBuild = [ pkg-config ];