Make the profiling detail level configurable with a flag

New flags: --profiling-detail and --library-profiling-detail.
When profiling is enabled (by the existing flags) then these flags
are taken into account to set the profiling detail level.

The levels are:
 none
 default
 exported-functions
 toplevel-functions
 all-functions

The default value for ghc for libraries is exported-functions and
for exes is toplevel-functions.

On GHC these levels correspond to the -fprof-auto* flags. The
ghc-prof-options will override this (just because it's passed to
ghc at the end).