mpv: Fix X11 support by adding libXrandr

This is a follow-up to 6b404b9, which
fixed the build after SDL no longer leaks through X libraries.

However the commit didn't actually pass all the required dependencies to
mpv, because the configure phase of mpv still disabled X support:

  Checking for X11
  err: Package xrandr was not found in the pkg-config search path.
  Perhaps you should add the directory containing `xrandr.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'xrandr' found

So by adding libXrandr, we finally have support for X again.

Trivia: While I'm usually very pesky about line lengths this is one of
the very rare occasions where I didn't break the lines after 79
characters because it would have messed up the overall style of the
file.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @AndersonTorres, @Fuuzetsu, @fpletz, @orivej

pkgs/applications/video/mpv/default.nix

@@ -7,7 +7,8 @@
     libGLU_combined       ? null,
     libX11     ? null,
     libXext    ? null,
-    libXxf86vm ? null
+    libXxf86vm ? null,
+    libXrandr  ? null
 
 , waylandSupport ? false
   , wayland           ? null
@@ -47,7 +48,7 @@ with stdenv.lib;
 let
   available = x: x != null;
 in
-assert x11Support         -> all available [libGLU_combined libX11 libXext libXxf86vm];
+assert x11Support         -> all available [libGLU_combined libX11 libXext libXxf86vm libXrandr];
 assert waylandSupport     -> all available [wayland wayland-protocols libxkbcommon];
 assert rubberbandSupport  -> available rubberband;
 assert xineramaSupport    -> x11Support && available libXinerama;
@@ -151,7 +152,7 @@ in stdenv.mkDerivation rec {
     ++ optional vapoursynthSupport vapoursynth
     ++ optional archiveSupport     libarchive
     ++ optionals dvdnavSupport     [ libdvdnav libdvdnav.libdvdread ]
-    ++ optionals x11Support        [ libX11 libXext libGLU_combined libXxf86vm ]
+    ++ optionals x11Support        [ libX11 libXext libGLU_combined libXxf86vm libXrandr ]
     ++ optionals waylandSupport    [ wayland wayland-protocols libxkbcommon ]
     ++ optionals stdenv.isDarwin (with darwin.apple_sdk.frameworks; [
       libiconv Cocoa CoreAudio