Add JS backend adapted from the GHCJS project by Luite Stegeman.

Some features haven't been ported or implemented yet. Tests for these
features have been disabled with an associated gitlab ticket.

Bump array submodule

Work funded by IOG.

Co-authored-by: Jeffrey Young <jeffrey.young@iohk.io>
Co-authored-by: Luite Stegeman <stegeman@gmail.com>
Co-authored-by: Josh Meredith <joshmeredith2008@gmail.com>

As noted in #16466, `System.Environment.getExecutablePath` depends upon
`PathFileExistsW` which is defined by `shlwapi`.

Fixes #16466.

Summary:
Another round and attempt at getting these down to 0.

We really should re-enable the CI and not wait for those cloud based ones.

I've disabled the backpack tests on windows as they are too broad, they test
as much the shell as they do the compiler.

The perf tests have been too long to track down. but the numbers are horrible
but I don't see them getting fixed so just have to accept them.

T9293 has new windows specific output because a Dyn way only flag was added.
This will of course not work on non-Dyn way builds.

Test Plan: ./validate

Reviewers: bgamari, hvr, simonmar

Reviewed By: bgamari

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #15107

Differential Revision: https://phabricator.haskell.org/D4668

It's a bit confusing to have .gitignore files spread all over the
filesystem. This commit tries to consolidate those into one .gitignore
file per component. Moreover, we try to describe files to be ignored which
happen to have a common identifying pattern by glob patterns.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

I used this shell command to automatically generate the lists:

for i in `git ls-files -o --exclude-standard --directory`; do echo "`basename $i`" >> "`dirname "$i"`/.gitignore"; done

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