[Yhc] can't build on MacOS?

[Malcolm Wallace]

OK, next problem.  Configure works fine, and 'make' builds the
compiler proper.  But building the prelude fails with:

  make -C src/prelude
  ../../inst/bin/yhc -d ../../inst/prelude System.hs
  Warning: the environment variable YHC_BASE_PATH is not set
  Fail: user error (Can't open any of:
    NHC/FFI.hi
    /include/NHC/FFI.hi
    when trying to read NHC.FFI.
  )

Regards,
    Malcolm