ghc from CVS HEAD doesn't work with "-O -threaded"

[Peter Simons]

The following reproducibly fails:

  $ darcs get http://cryp.to/hsdns      [*]
  $ cd hsdns/
  $ hsc2hs ADNS.hsc
  $ ghc -threaded -Wall -O --make test.hs -o test -ladns
  | Chasing modules from: test.hs
  | Compiling ADNS             ( ./ADNS.hs, ./ADNS.o )
  | /tmp/ghc2613.hc:9:23: ADNS_stub.h: No such file or directory
  | /tmp/ghc2613.hc: In function `s8Xa_ret':
  | /tmp/ghc2613.hc:6340: error: `ADNS_d7eN' undeclared (...)

If you build the program without optimization,

  $ ghc -threaded --make test -ladns

it works just fine. This seems to happen only when the
threaded RTS in involved, -O without -threaded works.

Peter