clang/wrapper cannot build GHC head with integer-gmp on Mavericks

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

Hi,

> Oh. Probably I was confused.
> 
> So, should we introduce a hack for Mavericks to gmp/ghc.mk?

OK. I created a patch:

	https://ghc.haskell.org/trac/ghc/ticket/8497#comment:8

With this patch, I can build GHC head/integer-gmp with GHC
7.6.3/clang-wrapper on Mavericks/XCode 5. (Note that patched alex and
happy are also necessary.)

--Kazu