lib/libffi: Add libffi as a submodule.

This allows to build libffi from source together with micropython, and is
useful for cross-compilation. Support for this was already merged
previously, to use:

make libffi
make MICROPY_STANDALONE=1

(To both commands appropriate cross-compilition flags can be added).

1 files changed, 0 insertions, 0 deletions

diff --git a/lib/libffi b/lib/libffi
new file mode 160000
+Subproject e9de7e35f2339598b16cbb375f9992643ed8120