A missing | meant that the build broke on machines that don't have
libgmp available.

Ian Lynagh <igloo@earth.li>**20100118191831

We were building GMP even if we didn't need to.

rolling back:

Sat Nov 21 16:43:13 EST 2009  Ben.Lippmeier@anu.edu.au
  * Windows DLLs: Tag imported gmp symbols with the package they're from.

    M ./cbits/gmp-wrappers.cmm -20 +20

- Needed to get arch-dependent options, eg, on Snow Leopard

Previously if you were to set HaveFrameworkGMP/HaveLibGmp in
mk/build.mk (e.g. on mac os) the settings would be ignored, as
gmp/config.mk is included late in GHC's ghc.mk, meaning autoconf
overrides your settings. Now they ignore the values picked up by 
configure if you set these variables.

This works around a crash (only on OS X for some reason?) where the GHCi
GMP uses the systems memory allocator. We should fix this properly, by
making ghci run constructor functions.