Apply SplitSections to all C compilations

Previously this was added only to the RTS's C files (those are the bulk
of it though), but there are C bits in ghc-prim, integer-gmp and base
too.

Followup for #8405, allows the large table of character properties in
base to be stripped when not used.

Test Plan: validate

Reviewers: austin, bgamari, simonmar

Reviewed By: bgamari

Subscribers: thomie, snowleopard

Differential Revision: https://phabricator.haskell.org/D3121