lang/ghc: Update to 8.4.3 and bump PORTREVISION's of all Haskell ports.

As usual, it is recommended to rebuild or reinstall all the
dependent ports and the lang/ghc port itself in one of the following
ways:

1. portmaster -w -r ghc or
2. portupgrade -fr lang/ghc

In case of pkg(8), it is probably safer to remove all the GHC-dependent
packages along with GHC and reinstall everything from scratch. For
example:

1. pkg query "%ro" ghc > ghc-pkgs.txt
2. pkg delete -y lang/ghc

In ghc-pkgs.txt, check and remove all the packages that have been moved
on the update, then use this command:

pkg install -y cat ghc-pkgs.txt

Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D16038