hadrian: enable building stage1 haddock for cross ghc

This commit enables building stage1 haddock for cross ghc. Without
this change, hadrian would panic with "Unknown program" error when
building the _build/stage1/bin/cross-prefix-haddock program needed by
the docs-haddock target, even if it only needs to copy from
_build/stage0/bin/cross-prefix-haddock.

(cherry picked from commit 272eaef0)

hadrian/src/Settings/Default.hs

@@ -156,6 +156,7 @@ stage1Packages = do
         , ghcInternal
         , ghcPkg
         , ghcPrim
+        , haddock
         , haskeline
         , hp2ps
         , hsc2hs
@@ -174,8 +175,7 @@ stage1Packages = do
         , if winTarget then win32 else unix
         ]
       , when (not cross)
-        [ haddock
-        , hpcBin
+        [ hpcBin
         , iserv
         , runGhc
         , ghcToolchainBin