ghc: Disable on AArch64

For some reason compiling the proper GHC from the binary one eventually
segfaults at some point.

Since it has never worked, just disable it and investigate later.

pkgs/development/compilers/ghc/8.2.1-binary.nix

@@ -158,5 +158,6 @@ stdenv.mkDerivation rec {
   passthru = { targetPrefix = ""; };
 
   meta.license = stdenv.lib.licenses.bsd3;
-  meta.platforms = ["x86_64-linux" "i686-linux" "x86_64-darwin" "armv7l-linux" "aarch64-linux"];
+  # AArch64 should work in theory but eventually some builds start segfaulting
+  meta.platforms = ["x86_64-linux" "i686-linux" "x86_64-darwin" "armv7l-linux" /* "aarch64-linux" */];
 }