kexectools: Add dependency on build CC

Seems to allow cross-compilation.

pkgs/os-specific/linux/kexectools/default.nix

···
-{ stdenv, fetchurl, zlib }:
+{ stdenv, buildPackages, fetchurl, zlib }:
 
 stdenv.mkDerivation rec {
   name = "kexec-tools-${version}";
···
 
   hardeningDisable = [ "format" "pic" "relro" ];
 
+  nativeBuildInputs = [ buildPackages.stdenv.cc ];
   buildInputs = [ zlib ];
 
   meta = with stdenv.lib; {