Declare "ghcjs-base" as a compiler-provided core package.

This change fixes several GHCJS-related packages in our Hackage database.

Cc: @Profpatsch

pkgs/development/haskell-modules/configuration-common.nix

@@ -4,6 +4,11 @@ with import ./lib.nix { inherit pkgs; };
 
 self: super: {
 
+  # Some Hackage packages reference this attribute, which exists only in the
+  # GHCJS package set. We provide a dummy version here to fix potential
+  # evaluation errors.
+  ghcjs-base = null;
+
   # Some packages need a non-core version of Cabal.
   cabal-install = super.cabal-install.overrideScope (self: super: { Cabal = self.Cabal_1_24_1_0; });
 

pkgs/development/haskell-modules/configuration-hackage2nix.yaml

@@ -31,6 +31,11 @@ core-packages:
   - unix-2.7.2.0
   - xhtml-3000.2.1
 
+  # Hack: The following package is a core package of GHCJS. If we don't declare
+  # it, then hackage2nix will generate a Hackage database where all dependants
+  # if this library are maked as "broken".
+  - ghcjs-base-0
+
 default-package-overrides:
   # LTS Haskell 7.9
   - abstract-deque ==0.3