Next libffi release

[Anthony Green <green at moxielogic dot com>]

There's been lots of activity over since last April, so I'd like to
get a new release out soon.  The README says:

	Add AArch64 support.
	Add Blackfin support.
	Add TILE-Gx/TILEPro support.
	Add Microblaze support.
	Add Xtensa support.
	Add support for PaX enabled kernels with MPROTECT.
	Add support for native vendor compilers on
	  Solaris and AIX.

There's one last thing I'd like to do before releaseing 3.0.12, which
is to move the headers into /usr/include.  The headers currently
install under /usr/lib/libffi-VERSION/include, and then users use
pkg-config to find the headers.  The main reason for this is that the
headers are modified at configure time, and I wanted to support
multiple ABIs on a single target (ie. mips o32, n32 and n64, in lib,
lib32 and lib64 respectively).  Installing header this way was
relatively common 10+ years ago, but it's just confusing to people
now.

The solution is to modify the headers to not rely on config time
changes, and to use a mess of target specific pre-defined compiler
macros in the headers to determine the target system.    I'm going to
give this a go, but it will impact every port so testing will be
important.

At the same time, I'm going to change all of the target macros from
things like X86 and ARM to LIBFFI_X86 and LIBFFI_ARM in order to
address namespace pollution.

AG