Figure out what to do about retainer profiling debugging code
rts/RetainerProfile.c has a hope pile of code guarded by the unset-by-default
DEBUG_RETAINER macro. I tried to resuscitate it while debugging #15287, but it seems like a bit of a lost cause. In particular, the
cost() function which seems to be critical to the accounting done by in this code was removed in dbef766c. While I can't tell for certain, it's possible that this "cost" notion coincides with the value currently computed by
Regardless, we should either drop this code if it's beyond saving or fix it to do something useful.