Depend on Stage2 GHC, ghc-pkg and hpc in validate target.

See #187. [skip ci]

src/Builder.hs

@@ -124,6 +124,8 @@ getBuilderPath = lift . builderPath
 specified :: Builder -> Action Bool
 specified = fmap (not . null) . builderPath
 
+-- TODO: split into two functions: needBuilder (without laxDependencies) and
+-- unsafeNeedBuilder (with the laxDependencies parameter)
 -- | Make sure a builder exists on the given path and rebuild it if out of date.
 -- If 'laxDependencies' is True then we do not rebuild GHC even if it is out of
 -- date (can save a lot of build time when changing GHC).

src/Test.hs

@@ -15,6 +15,9 @@ import Settings.User
 testRules :: Rules ()
 testRules = do
     "validate" ~> do
+        needBuilder False $ Ghc Stage2 -- TODO: get rid of False parameters
+        needBuilder False $ GhcPkg Stage1
+        needBuilder False $ Hpc
         runMakeVerbose "testsuite/tests" ["fast"]
 
     "test" ~> do