cramfsprogs: support cross-compilation

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

@@ -16,6 +16,10 @@ stdenv.mkDerivation rec {
   # So patch the "missing include" bug ourselves.
   patches = [ ./include-sysmacros.patch ];
 
+  makeFlags = [
+    "CC=${stdenv.cc.targetPrefix}cc"
+  ];
+
   installPhase = ''
     install --target $out/bin -D cramfsck mkcramfs
   '';