arm64: 64bit iOS and SMP support (#7942)

Signed-off-by: Austin Seipp <austin@well-typed.com>
ghc generates more user-friendly error messages

Test Plan: Compiled ghc fine.  Opened ghci and fed it invalid code.  It gave the improved error messages in response.

Reviewers: austin

Subscribers: thomie, simonpj, spacekitteh, rwbarton, simonmar, carter

Differential Revision: https://phabricator.haskell.org/D201
Make calling conventions in template haskell Syntax.hs consistent with those in ghc ForeignCall.hs
this impliments #9703 from ghc trac

Test Plan: still needs tests

Reviewers: cmsaperstein, ekmett, goldfire, austin

Reviewed By: goldfire, austin

Subscribers: goldfire, thomie, carter, simonmar

Differential Revision: https://phabricator.haskell.org/D353

GHC Trac Issues: #9703