Cabal on multiple platforms

[Henning Thielemann]

The current directory structure under 'dist/build' does not allow for
sharing source code on multiple machines. I thought it would be a good
idea to insert a directory layer for the target machine. Then I can use
the same sources and haddock files on multiple machines which mount the
same filesystem. Cabal could create, say

dist
  build
    Linux-ix86
    Linux-PPC
    Solaris-ix86
    Solaris-MIPS
  doc
    html

.