treewide: use gnu toolchain for avr/arm-embedded

These packages should in theory work with our GCC toolchains, but
there are some definite breakages that need to be tracked down.
Comparing output of these to old gcc-arm-embedded is important.

Affected packages include:

- axolooti
- avrdudess
- opentx
- microscheme
- betaflight
- inav
- blackmagic
- simavr
- gnuk

pkgs/development/tools/misc/blackmagic/default.nix

@@ -1,5 +1,5 @@
 { stdenv, lib, fetchFromGitHub
-, gcc-arm-embedded, libftdi
+, gcc-arm-embedded, binutils-arm-embedded, libftdi
 , python, pythonPackages
 }:
 
@@ -17,8 +17,11 @@ stdenv.mkDerivation rec {
     fetchSubmodules = true;
   };
 
+  nativeBuildInputs = [
+    gcc-arm-embedded binutils-arm-embedded
+  ];
+
   buildInputs = [
-    gcc-arm-embedded
     libftdi
     python
     pythonPackages.intelhex