libglvnd: Improve the license information (#114466)

Unfortunately the upstream licensing is quite complicated:
https://gitlab.freedesktop.org/glvnd/libglvnd#libglvnd

The main libglvnd license is MIT-like but files under different licenses
are also included. This is an approximation that ignores some license
"customizations".

Other distributions use the following license specifications:
- "MIT":
  - https://src.fedoraproject.org/rpms/libglvnd/blob/rawhide/f/libglvnd.spec
  - https://build.opensuse.org/package/view_file/openSUSE:Factory/libglvnd/libglvnd.spec
  - https://gitweb.gentoo.org/repo/gentoo.git/tree/media-libs/libglvnd/libglvnd-1.3.2-r2.ebuild
- "custom:MIT-alike": https://github.com/void-linux/void-packages/blob/master/srcpkgs/libglvnd/template
- "APACHE20 MIT": https://www.freshports.org/graphics/libglvnd
- "custom:BSD-like": https://archlinux.org/packages/extra/x86_64/libglvnd/

pkgs/development/libraries/libglvnd/default.nix

@@ -62,7 +62,8 @@ stdenv.mkDerivation rec {
       Both GLX and EGL are supported, in any combination with OpenGL and OpenGL ES.
     '';
     inherit (src.meta) homepage;
-    license = licenses.bsd2;
+    # https://gitlab.freedesktop.org/glvnd/libglvnd#libglvnd:
+    license = with licenses; [ mit bsd1 bsd3 gpl3Only asl20 ];
     platforms = platforms.linux ++ platforms.darwin;
     maintainers = with maintainers; [ primeos ];
   };