Allow libffi snapshots

Authored by Moritz Angermann <moritz.angermann@gmail.com> on Sep 30 2017, 8:31 AM.

Description

Allow libffi snapshots

This is rather annoying. I'd prefer to have a stable release to
use. However libffi-3.2.1 has been released November 12, 2014, and
libffi-4 is TBD. See also https://github.com/libffi/libffi/issues/296

The core reason for this change is that llvm changed the supported
assembly to unified syntax, which libffi-3.2.1 does not use, and hence
fails to compile for arm with llvm. For refence, see the following
issue: https://github.com/libffi/libffi/issues/191.

This diff contains a script to generate a tarball for the
libffi-tarballs repository from the libffi GitHub repository; as well
as the necessary changes to the build system.

Updates libffi-tarballs submodule.

Reviewers: austin, bgamari, hvr

Subscribers: hvr, erikd, rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3574

bgamari committed rGHCDIFFe515c7f37be9: Allow libffi snapshots (authored by Moritz Angermann <moritz.angermann@gmail.com>).Sep 30 2017, 10:17 AM