Implement split-sections support for windows.
Initial implementation of split-section on Windows.
This also corrects section namings and uses the platform
convention of $ instead of . to separate sections.
Implementation is based on @awson's patches to binutils.
Binutils requires some extra help when compiling the libraries
for GHCi usage. We drop the -T and use implicit scripts to amend
the linker scripts instead of replacing it.
Because of these very large GHCi object files, we need big-obj support,
which will be added by another patch.
Test Plan: ./validate
Reviewers: awson, austin, bgamari
Subscribers: dfeuer, rwbarton, thomie, snowleopard, #ghc_windows_task_force
GHC Trac Issues: Trac #12913
Differential Revision: https://phabricator.haskell.org/D3383