Add OpenRISC support

This patch adds support for the OpenRISC architecture.
(http://opencores.org/or1k/Main_Page)

The code has been tested under Linux with QEMU-user emulation support.
- 32 Bit
- big endian
- delayed instructions
This is the only available configuration under Linux.

The description of the ABI can be found on the official website.

It passes the testsuite except of the unwindtest_ffi_call.cc testcase, 
which seems to be a problem of gcc and not of libffi.
The OpenRISC support in gcc is not complete yet.

Signed-off-by: Sebastian Macke <sebastian@macke.de>