Add ARC support

This adds support for the ARC architecture to libffi. DesignWare ARC
is a family of processors from Synopsys, Inc.

This patch has been tested on a little-endian system and passes
the testsuite.

Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
Merge pull request #44 from foss-for-synopsys-dwc-arc-processors/arc_support

Add ARC support