haskell.packages.{ghc96,ghc98}: disable haddock for cross

In this situation, haddock would not be built by hadrian, as there is no
stage0:exe:haddock target by default. (We should eventually try adding
one.) If haddock is enabled and the build->host haddock missing, Cabal
tries using the build->build haddock which may fail to load the
documentation from the interface files produced by the build->host
GHC (e.g. due to a mismatch between dynamic and static linking).

Add regression tests to haskell-updates jobset.

Resolves #275304.

pkgs/development/compilers/ghc/common-hadrian.nix

@@ -507,6 +507,10 @@ stdenv.mkDerivation ({
 
     # Expose hadrian used for bootstrapping, for debugging purposes
     inherit hadrian;
+
+    # TODO(@sternenseemann): there's no stage0:exe:haddock target by default,
+    # so haddock isn't available for GHC cross-compilers. Can we fix that?
+    hasHaddock = stdenv.hostPlatform == stdenv.targetPlatform;
   };
 
   meta = {

pkgs/top-level/release-haskell.nix

@@ -448,6 +448,15 @@ let
                 xhtml # isn't bundled for cross
               ;
             };
+
+            haskell.packages.native-bignum.ghc981 = {
+              inherit (packagePlatforms pkgs.pkgsStatic.haskell.packages.native-bignum.ghc981)
+                hello
+                random
+                QuickCheck
+                terminfo # isn't bundled for cross
+                ;
+            };
           };
 
       pkgsCross.ghcjs =
@@ -673,6 +682,7 @@ let
         constituents = accumulateDerivations [
           jobs.pkgsStatic.haskell.packages.native-bignum.ghc948 # non-hadrian
           jobs.pkgsStatic.haskellPackages
+          jobs.pkgsStatic.haskell.packages.native-bignum.ghc981
         ];
       };
     }