Make globals use sharedCAF

Summary:
The use of globals is quite painful when multiple rts are loaded, e.g.
when plugins are loaded, which bring in a second rts. The sharedCAF
appraoch was employed for the FastStringTable; I've taken the libery
to extend this to the other globals I could find.

This is a reboot of D2575, that should hopefully not exhibit the same
windows build issues.

Reviewers: Phyx, simonmar, goldfire, bgamari, austin, hvr, erikd

Reviewed By: Phyx, simonmar, bgamari

Subscribers: mpickering, thomie

Differential Revision: https://phabricator.haskell.org/D2773