Deduplicate decision to count thunks in -ticky
Previously, the logic that checks whether a thunk has a counter or not
was duplicated in multiple functions.
This led to thunk enters being accounted to their enclosing functions in
StgCmmTicky.tickyEnterThunk, because the outer call to
withNewTickyCounterThunk didn't set the counter label for the thunk.
And rightly so! tickyEnterThunk should only account thunk enters to a
counter if -ticky-dyn-thunk is on.
This patch extracts the logic that was already present in its most
general form in withNewTickyCounterThunk into its own functions and
lets all other call sites checking for -ticky-dyn-thunk call this new
function named thunkHasCounter instead.
Reviewers: bgamari, simonmar
Reviewed By: simonmar
Subscribers: rwbarton, carter
Differential Revision: https://phabricator.haskell.org/D5392