DsMeta does not attempt to handle quasiquoted Char# or Addr# values,
which causes expressions like `$([| 'a'# |])` or `$([| "abc"# |])` to
fail
with an `Exotic literal not (yet) handled by Template Haskell` error.

To fix this, the API of `template-haskell` had to be changed so that
`Lit`
now has an extra constructor `CharPrimL` (a `StringPrimL` constructor
already
existed, but it wasn't used). In addition, `DsMeta` has to manipulate
`CoreExpr`s directly that involve `Word8`s. In order to do this,
`Word8` had
to be added as a wired-in type to `TysWiredIn`.

Actually converting from `HsCharPrim` and `HsStringPrim` to `CharPrimL`
and
`StringPrimL`, respectively, is pretty straightforward after that, since
both `HsCharPrim` and `CharPrimL` use `Char` internally, and
`HsStringPrim`
uses a `ByteString` internally, which can easily be converted to
`[Word8]`,
which is what `StringPrimL` uses.

Reviewers: goldfire, austin, simonpj, bgamari

Reviewed By: simonpj, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1054

GHC Trac Issues: #10620