Cleanup the QC.hs file w.r.t. compiler options

Currently, we build the Haskell unittests with custom GHC flags,
because we (I) were quite lazy when initially writing the
unittests. This is not a problem for the tests themselves, but it
creates problem when (for example) one would want to pass all
$(HS_LIB_SRCS) to the compilers; this is not doable unless we
"degrade" the flags used for all modules, instead of just for QC.hs.

So we do two things to fix this:

- first, we go and add type declaration to all functions that were
  missing them (in QC), and fix the couple of cases of monomorphism
  restrictions; this gets us rid of -fno-warn-missing-signature and
  -fno-warn-monomorphism-restriction
- then, we move the actually important remaining options
  (-fno-warn-orphans and -fno-warn-unused-imports; see the explanation
  for the latter in the newly added FIXME) to a compiler pragma in the
  file, so that when building the unittests only this file is using
  the extra options

And finally we can then drop the other unused options
(-fno-warn-missing-methods anmd -Wwarn), leaving htools/test use
simply -fhpc. This is more in-line with the other files, and thus we
can handle all of HS_LIB_SRCS the same.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>