Summary:
This commit adds stage 1 support for Template Haskell
quoting, e.g. [| ... expr ... |], which is useful
for authors of quasiquoter libraries that do not actually
need splices.  The TemplateHaskell extension now does not
unconditionally fail; it only fails if the renamer encounters
a splice that it can't run.

In order to make sure the referenced data structures
are consistent, template-haskell is now a boot library.
There are some minor BC changes to template-haskell to make it boot
on GHC 7.8.

Note for reviewer: big diff changes are simply code
being moved out of an ifdef; there was no other substantive
change to that code.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: simonpj, austin, goldfire

Subscribers: bgamari, thomie

Differential Revision: https://phabricator.haskell.org/D876

GHC Trac Issues: #10382