Summary:
This applies a patch from Reid Barton and Sylvain Henry, which fix a
disasterous infinite loop when iconv fails to load locale files, as
specified in #10298.

The fix is a bit of a hack but should be fine - for the actual reasoning
behind it, see `Note [Disaster and iconv]` for more info.

In addition to this fix, we also patch up the IO Encoding utilities to
recognize several variations of the 'ASCII' encoding (including its
aliases) directly so that GHC can do conversions without iconv. This
allows a static binary to sit in an initramfs.

Authored-by: Reid Barton <rwbarton@gmail.com>
Authored-by: Sylvain Henry <hsyl20@gmail.com>
Signed-off-by: Austin Seipp <austin@well-typed.com>

Test Plan: Eyeballed it.

Reviewers: rwbarton, hvr

Subscribers: bgamari, thomie

Differential Revision: https://phabricator.haskell.org/D898

GHC Trac Issues: #10298, #7695