idrisPackages.glfw: Fix runtime

In order to run programs, pkgconfig needs to be present so it can tell
it where to find glfw3 and gl.

pkgs/development/idris-modules/glfw.nix

@@ -10,8 +10,14 @@ build-idris-package  {
 
   idrisDeps = [ effects ];
 
+  nativeBuildInputs = [ pkgs.pkgconfig ];
   extraBuildInputs = [ pkgs.glfw ];
 
+  postPatch = ''
+    substituteInPlace src/MakefileGlfw \
+      --replace glfw3 "glfw3 gl"
+  '';
+
   src = fetchFromGitHub {
     owner = "eckart";
     repo = "glfw-idris";