Fix #line pragmas in nested comments

Authored by bsklaroff on Aug 21 2018, 11:03 AM.

Description

Fix #line pragmas in nested comments

When parsing a nested comment or nested doc comment in the lexer, if we
see a line starting with '#' we attempt to parse a #line pragma. This
fixes how ghc handles output of the C preproccesor (-cpp flag) when the
original source has C comments or pragmas inside haskell comments.

Updates haddock submodule.

Test Plan: ./validate

Reviewers: bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: Trac #314

Differential Revision: https://phabricator.haskell.org/D4934