avr: use new compilation infrastructure

Gets rid of:
  avrbinutils
  avrgcc

to replace with:
  pkgsCross.avr.buildPackages.binutils
  pkgsCross.avr.buildPackages.gcc

pkgs/development/misc/avr/libc/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, avrgcc, avrbinutils, automake, autoconf }:
+{ stdenv, fetchurl, automake, autoconf }:
 
 let
   version = "2.0.0";
@@ -11,18 +11,7 @@ stdenv.mkDerivation {
     sha256 = "15svr2fx8j6prql2il2fc0ppwlv50rpmyckaxx38d3gxxv97zpdj";
   };
 
-  buildInputs = [ avrgcc avrbinutils automake autoconf ];
-  configurePhase = ''
-    unset LD
-    unset AS
-    unset AR
-    unset CC
-    unset CXX
-    unset RANLIB
-    unset STRIP
-
-    ./configure --prefix=$out --build=$(./config.guess) --host=avr
-  '';
+  nativeBuildInputs = [ automake autoconf ];
 
   # Make sure we don't strip the libraries in lib/gcc/avr.
   stripDebugList= "bin";
@@ -32,7 +21,7 @@ stdenv.mkDerivation {
     description = "a C runtime library for AVR microcontrollers";
     homepage = http://savannah.nongnu.org/projects/avr-libc/;
     license = licenses.bsd3;
-    platforms = platforms.unix;
+    platforms = platforms.all;
     maintainers = with maintainers; [ mguentner ];
   };
 }