Summary:
There was a broken offset calculation that only worked when the
sections of the binary were in a particular order, and this
broke (sometimes) after we started mapping the sections separately in
the linker (see D975).

Test Plan: ghci debugger tests now work with DYNAMIC_GHC_PROGRAMS=NO

Reviewers: austin, hvr, bgamari, erikd

Reviewed By: bgamari

Subscribers: Phyx, thomie, trommler

Differential Revision: https://phabricator.haskell.org/D1346

GHC Trac Issues: #10994