GHC 8.4 is expected to ship with an updated GCC bindist based on GCC 7.2.
I am however at this time not updating the crt due to an issue introduced
in september. https://sourceforge.net/p/mingw-w64/mailman/message/36085637/
Unless a favorable fix comes out of the discussion I will just ship the old crt
with GHC 8.4.