GHC (as of version 4.00) supports Concurrent Haskell by default, without requiring a special option or libraries compiled in a certain way. To get access to the support libraries for Concurrent Haskell (i.e. Concurrent and friends), use the -syslib concurrent option.
Three RTS options are provided for modifying the behaviour of the threaded runtime system. See the descriptions of -C[<us>], -q, and -t<num> in Section 3.11.4.
Concurrent Haskell is described in more detail in Section 6.12.