Remove overlay/ghc.nix

It breaks the `override` function on the ghc compilers and it only serves to add "stackprotector" to `hardeningDisable`.  We can just add that to `compiler/ghc/default.nix`.

It looks like it also added "format", but that is already present.  For `hostPlatform.isAarch32` it adds "pie" (not already present), but we don't build GHC on 32bit arm.

Author: hamishmack

compiler/ghc/default.nix

@@ -546,7 +546,7 @@ stdenv.mkDerivation (rec {
 
   checkTarget = "test";
 
-  hardeningDisable = [ "format" ]
+  hardeningDisable = [ "format" "stackprotector" ]
                    ++ lib.optional stdenv.targetPlatform.isAarch32 "pic"
                    ++ lib.optional stdenv.targetPlatform.isMusl "pie"
                    ++ lib.optional enableDWARF "fortify";

overlays/default.nix

@@ -76,7 +76,6 @@ let
 
     bootstrap = import ./bootstrap.nix;
     compiler-llvm = import ./compiler-llvm.nix;
-    ghc = import ./ghc.nix;
     ghc-packages = import ./ghc-packages.nix;
     darwin = import ./darwin.nix;
     windows = import ./windows.nix;
@@ -114,7 +113,6 @@ let
     nix-tools
     bootstrap
     compiler-llvm
-    ghc
     ghc-packages
     darwin
     windows