rkdeveloptool: fix build on darwin

pkgs/by-name/rk/rkdeveloptool/package.nix

@@ -26,7 +26,9 @@ stdenv.mkDerivation {
   buildInputs = [ libusb1 ];
 
   # main.cpp:1568:36: error: '%s' directive output may be truncated writing up to 557 bytes into a region of size 5
-  CPPFLAGS = lib.optionals stdenv.cc.isGNU [ "-Wno-error=format-truncation" ];
+  CPPFLAGS =
+    lib.optionals stdenv.cc.isGNU [ "-Wno-error=format-truncation" ]
+    ++ lib.optionals stdenv.isDarwin [ "-Wno-error=vla-cxx-extension" ];
 
   meta = with lib; {
     homepage = "https://github.com/rockchip-linux/rkdeveloptool";