Omit unnecessary linker flags

Summary:
This omits -L and -l flags from the linker command line that shouldn't
be necessary because GHC will already add them via the -package-id
flags we pass.

This also reverts part of 90538d86
that rearranges the linker command line and causes some knock-on
problems (see D2618).

Test Plan: validate (need to validate on Windows too)

Reviewers: Phyx, bgamari, niteria, austin, erikd

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2639

GHC Trac Issues: #12738