[project @ 1999-03-03 19:26:31 by sof]

COMPILING_RTS is now defined when compiling the rts. It is used for
the following:

 - the contents of includes/Prelude.h is only visible when COMPILING_RTS
   is on.
 - getting the DLLIMPORT declarations right on various labels defined by
   the Prelude or the RTS.