Update libffi

Updates the libffi to version 3.1 in order to support the ppc64le architecture.
Fix HAVE_LONG_DOUBLE_VARIANT undefined error

Applied the fix to this issue created by Matthias Klose.

https://launchpad.net/ubuntu/+source/libffi/3.1-2
Define CPU for ppc64le.
Add PowerPC64 little endian support

Adds support for the ppc64le architecture.

Conflicts:
	src/main/java/com/kenai/jffi/Platform.java
	src/main/java/com/kenai/jffi/internal/StubLoader.java