Clean up RTS Linker Windows.

Clean up the linker code for PE.

1. Stop copying structures from the windows header
   and use those that are in the headers. There's no
   point in copying them and we got a few types wrong.

2. Replace custom typedef with C99 types. If we're not
   going to use the Windows type aliases, at least use
   standard ones.

Test Plan: ./validate

Reviewers: simonmar, austin, erikd, bgamari

Reviewed By: simonmar, bgamari

Subscribers: dfeuer, thomie, #ghc_windows_task_force

Differential Revision: https://phabricator.haskell.org/D2944