haskell.packages.ghc865Binary: drop unevaluatable packages

`haskell.packages.ghc865Binary` has a few packages that fails to evaluate
by referring non-existent attributes. This turns evaluation attempts into
unrecoverable errors.

Before the change an attempt to instantiate all `ghc810` packages failed
as:

    $ nix-instantiate --strict --eval --expr 'with import ./. {}; lib.mapAttrs (n: v: builtins.tryEval (lib.isDerivation v)) haskell.packages.ghc865Binary'
    error:
       … while evaluating the attribute 'llvmPackages'

         at lib/attrsets.nix:1180:11:

         1179|     attrs:
         1180|     attrs // { recurseForDerivations = false; };
             |           ^
         1181|

       error: value is null while a set was expected

The change follows definition of `pkgs/top-level/haskell-packages.nix`
and also sets `llvmPackages` to `null`. While at it dropped other
references to deleted packages like `exceptions` pin.

pkgs/development/haskell-modules/configuration-ghc-8.6.x.nix

@@ -8,7 +8,8 @@ in
 
 self: super: {
 
-  llvmPackages = pkgs.lib.dontRecurseIntoAttrs self.ghc.llvmPackages;
+  # Should be llvmPackages_6 which has been removed from nixpkgs
+  llvmPackages = null;
 
   # Disable GHC 8.6.x core libraries.
   array = null;
@@ -49,6 +50,9 @@ self: super: {
 
   # Need the Cabal-syntax-3.6.0.0 fake package for Cabal < 3.8 to allow callPackage and the constraint solver to work
   Cabal-syntax = self.Cabal-syntax_3_6_0_0;
+  # These core package only exist for GHC >= 9.4. The best we can do is feign
+  # their existence to callPackages, but their is no shim for lower GHC versions.
+  system-cxx-std-lib = null;
 
   # Needs Cabal 3.0.x.
   jailbreak-cabal = super.jailbreak-cabal.overrideScope (cself: _: { Cabal = cself.Cabal_3_2_1_0; });
@@ -91,7 +95,7 @@ self: super: {
   ghc-lib-parser-ex = addBuildDepend self.ghc-lib-parser super.ghc-lib-parser-ex;
 
   # This became a core library in ghc 8.10., so we don’t have an "exception" attribute anymore.
-  exceptions = super.exceptions_0_10_4;
+  exceptions = null;
 
   # Older compilers need the latest ghc-lib to build this package.
   hls-hlint-plugin = addBuildDepend self.ghc-lib super.hls-hlint-plugin;