initial implementation of vc4 cross-compile

pkgs/development/compilers/gcc/6/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, targetPackages, fetchurl, fetchpatch, noSysDirs
+{ stdenv, targetPackages, fetchurl, fetchpatch, fetchFromGitHub, noSysDirs
 , langC ? true, langCC ? true, langFortran ? false
 , langObjC ? stdenv.targetPlatform.isDarwin
 , langObjCpp ? stdenv.targetPlatform.isDarwin
@@ -9,6 +9,7 @@
 , enableShared ? true
 , enableLTO ? true
 , texinfo ? null
+, flex
 , perl ? null # optional, for texi2pod (then pod2man); required for Java
 , gmp, mpfr, libmpc, gettext, which
 , libelf                      # optional, for link-time optimizations (LTO)
@@ -107,7 +108,12 @@ stdenv.mkDerivation ({
 
   builder = ../builder.sh;
 
-  src = fetchurl {
+  src = if stdenv.targetPlatform.isVc4 then fetchFromGitHub {
+    owner = "itszor";
+    repo = "gcc-vc4";
+    rev = "e90ff43f9671c760cf0d1dd62f569a0fb9bf8918";
+    sha256 = "0gxf66hwqk26h8f853sybphqa5ca0cva2kmrw5jsiv6139g0qnp8";
+  } else fetchurl {
     url = "mirror://gnu/gcc/gcc-${version}/gcc-${version}.tar.xz";
     sha256 = "0i89fksfp6wr1xg9l8296aslcymv2idn60ip31wr9s4pwin7kwby";
   };
@@ -172,7 +178,8 @@ stdenv.mkDerivation ({
   depsBuildBuild = [ buildPackages.stdenv.cc ];
   nativeBuildInputs = [ texinfo which gettext ]
     ++ (optional (perl != null) perl)
-    ++ (optional javaAwtGtk pkgconfig);
+    ++ (optional javaAwtGtk pkgconfig)
+    ++ (optional (stdenv.targetPlatform.isVc4) flex);
 
   # For building runtime libs
   depsBuildTarget =