mesa: 21.0.1 -> 21.0.3

Note: The update to Mesa 21.0.2 was reverted (25ae1fd29f) because it
caused major issues with Sway (segfault on startup [0]).
This is still the case and might affect all packages that directly
depend on "mesa" (for libgbm or libglapi) but it only causes issues when
the package depends on a "mesa" version that differs from "mesa.drivers"
used for "/run/opengl-driver/". I've noticed this while testing Mesa
updates with the NixOS option "hardware.opengl.package" (as usual)
instead of rebuilding my whole system (which would work). Unfortunately
this can/will likely also cause issues when mixing different channels,
using Flakes/Overlays, etc.

The cause of this should be similar to [1] ("mesa" updates now cause the
same issues that "glibc" updates already do, maybe triggered by certain
Mesa changes) and some additional discussions is in [2],[3].

Note: Don't backport this to NixOS 21.05, at least not without careful
consideration.

[0]: https://github.com/NixOS/nixpkgs/pull/118753#issuecomment-818950977
[1]: https://github.com/NixOS/nixpkgs/issues/95808
[2]: https://github.com/NixOS/nixpkgs/pull/120325
[3]: https://github.com/NixOS/nixpkgs/pull/119558

pkgs/development/libraries/mesa/default.nix

@@ -31,7 +31,7 @@ with lib;
 let
   # Release calendar: https://www.mesa3d.org/release-calendar.html
   # Release frequency: https://www.mesa3d.org/releasing.html#schedule
-  version = "21.0.1";
+  version = "21.0.3";
   branch  = versions.major version;
 
 self = stdenv.mkDerivation {
@@ -45,7 +45,7 @@ self = stdenv.mkDerivation {
       "ftp://ftp.freedesktop.org/pub/mesa/${version}/mesa-${version}.tar.xz"
       "ftp://ftp.freedesktop.org/pub/mesa/older-versions/${branch}.x/${version}/mesa-${version}.tar.xz"
     ];
-    sha256 = "1fqj2xhhd1ary0pfg31jq6fqcnd6qgyrw1445nmz554k8n2ck7rp";
+    sha256 = "0awiyvicvcn3b18x0vx5ik3ly0k3k51ivz2ljj8pnx6ms95nyp2n";
   };
 
   prePatch = "patchShebangs .";