Merge branch 'staging' into gcc-7

pkgs/os-specific/linux/kernel-headers/default.nix

···
   };
 in {
 
-  linuxHeaders_4_4 = common {
-    version = "4.4.10";
-    sha256 = "1kpjvvd9q9wwr3314q5ymvxii4dv2d27295bzly225wlc552xhja";
-  };
-
-  linuxHeaders_4_15 = common {
+  linuxHeaders = common {
     version = "4.15";
     sha256 = "0sd7l9n9h7vf9c6gd6ciji28hawda60yj0llh17my06m0s4lf9js";
   };

pkgs/top-level/all-packages.nix

···
   lkl = callPackage ../applications/virtualization/lkl { };
 
   inherit (callPackages ../os-specific/linux/kernel-headers { })
-    linuxHeaders_4_4 linuxHeaders_4_15;
-  linuxHeaders = if hostPlatform.isMusl || hostPlatform.isRiscV then linuxHeaders_4_15 else linuxHeaders_4_4;
+    linuxHeaders;
 
   kernelPatches = callPackage ../os-specific/linux/kernel/patches.nix { };