patch applied (ghc): mmap() errors on Darwin: use errorBelch/exit instead of barf()

[Simon Marlow]

Mon Feb 27 03:11:03 PST 2006  Simon Marlow <simonmar at microsoft.com>
  * mmap() errors on Darwin: use errorBelch/exit instead of barf()
  
  The most likely cause is out-of-memory, not an RTS error.

    M ./ghc/rts/MBlock.c -3 +7