opencl-headers: use cmake build

This is makes the build process simpler and exports .cmake
and pkg-config(.pc) files

pkgs/development/libraries/opencl-headers/default.nix

@@ -1,4 +1,7 @@
-{ lib, stdenv, fetchFromGitHub
+{ lib
+, stdenv
+, fetchFromGitHub
+, cmake
 }:
 
 stdenv.mkDerivation rec {
@@ -12,10 +15,7 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-BJDaDokyHgmyl+bGqCwG1J7iOvu0E3P3iYZ1/krot8s=";
   };
 
-  installPhase = ''
-    mkdir -p $out/include/CL
-    cp CL/* $out/include/CL
-  '';
+  nativeBuildInputs = [ cmake ];
 
   meta = with lib; {
     description = "Khronos OpenCL headers version ${version}";