PS: AMP (#8004) almost finished, review would be nice

[David Luposchainsky]

A user in #ghc noticed the patches I provided were hard to read due to
the unrelated whitespace changes. I scolded my editor for cleaning up
automatically and reverted the whitespace changes, the new version can
be found here:

https://github.com/quchen/ghc/compare/ghc:master...amp_warnings?expand=1

Sorry for the inconvenience,
David/quchen