i3lock-blur: add libGL build input

Currently, this is propagated from cairo, but that will soon no longer
be the case.

pkgs/applications/window-managers/i3/lock-blur.nix

@@ -1,4 +1,4 @@
-{ i3lock-color, lib, stdenv, fetchFromGitHub, fetchpatch }:
+{ i3lock-color, lib, stdenv, fetchFromGitHub, fetchpatch, libGL }:
 
 i3lock-color.overrideAttrs (oldAttrs : rec {
   pname = "i3lock-blur";
@@ -21,6 +21,8 @@ i3lock-color.overrideAttrs (oldAttrs : rec {
     })
   ];
 
+  buildInputs = oldAttrs.buildInputs ++ [ libGL ];
+
   meta = with lib; {
     description = "An improved screenlocker based upon XCB and PAM with background blurring filter";
     homepage = "https://github.com/karulont/i3lock-blur/";