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/misc/newlib/default.nix

@@ -23,12 +23,13 @@ in stdenv.mkDerivation {
     "--disable-nls"
     "--enable-newlib-io-long-long"
     "--enable-newlib-register-fini"
+    "--enable-newlib-retargetable-locking"
   ];
 
   dontDisableStatic = true;
 
   passthru = {
-    incdir = "/${stdenv.hostPlatform.config}/include";
-    libdir = "/${stdenv.hostPlatform.config}/lib";
+    incdir = "/${stdenv.targetPlatform.config}/include";
+    libdir = "/${stdenv.targetPlatform.config}/lib";
   };
 }