libffi via submodule

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

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie, snowleopard

Differential Revision: https://phabricator.haskell.org/D3349

1 files changed, 0 insertions, 0 deletions

diff --git a/libffi-tarballs b/libffi-tarballs
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-Subproject ec37a68838566cb830c33cb30bfade003a306cf