Fix #8754 in a round-about way.

For some reason on OS X, it seems like -Bsymbolic (which we use for
hooks into the RTS) isn't working, which results in #8754, where stats
don't work because defaultHooks doesn't initialize the stats flag. This
seems to work on Linux static/dynamically, but only on OS X statically.

After talking with Simon, really, the entire hooks thing is a bit
fragile. For now, we just work around it (since GHCi is dynamically
linked) by calling into the defaultHooks ourselves when GHC starts.
Signed-off-by: Austin Seipp <austin@well-typed.com>

ghc/Main.hs

 {-# OPTIONS -fno-warn-incomplete-patterns -optc-DNON_POSIX_SOURCE #-}
+{-# LANGUAGE ForeignFunctionInterface #-}
 
 -----------------------------------------------------------------------------
 --
@@ -76,6 +77,7 @@ import Data.Maybe
 
 main :: IO ()
 main = do
+   defaultsHook
    hSetBuffering stdout LineBuffering
    hSetBuffering stderr LineBuffering
    GHC.defaultErrorHandler defaultFatalMessager defaultFlushOut $ do
@@ -818,3 +820,5 @@ unknownFlagsErr fs = throwGhcException $ UsageError $ concatMap oneError fs
         (case fuzzyMatch f (nub allFlags) of
             [] -> ""
             suggs -> "did you mean one of:\n" ++ unlines (map ("  " ++) suggs)) 
+
+foreign import ccall safe "defaultsHook" defaultsHook :: IO ()