Building GHC head with clang on Mavericks

[Kazu Yamamoto (=?iso-2022-jp?B?GyRCOzNLXE9CSScbKEI=?=)]

> So did you find a bug in the current design of the clang-wrapper hack? 

No. What I found is that the current design of the clang-wrapper hack
is appropriate.

"-x assembler-with-cpp" is necessary to rescue
----
{-# RULE whatever
  #-}
---

> If so it'd be better to get it fixed there rather than in the
> Alex/happy setup HS files.

If we can do this, it's very good. But this is not good enough. 
happy/alex hack are also necessary to not generate
----
 # 1 "<built-inxxx>" 1

 # 1 "templates/GenericTemplatexxx.hs" 2
----

--Kazu