Revert "lib: Clean up how linux and gcc config is specified"

This is a stdenv-rebuild, and should not be merged
into master

This reverts commit 8929989614.

nixos/modules/installer/netboot/netboot.nix

@@ -88,7 +88,7 @@ with lib;
 
     system.build.netbootIpxeScript = pkgs.writeTextDir "netboot.ipxe" ''
       #!ipxe
-      kernel ${pkgs.stdenv.hostPlatform.linux-kernel.target} init=${config.system.build.toplevel}/init initrd=initrd ${toString config.boot.kernelParams}
+      kernel ${pkgs.stdenv.hostPlatform.platform.kernelTarget} init=${config.system.build.toplevel}/init initrd=initrd ${toString config.boot.kernelParams}
       initrd initrd
       boot
     '';