[PATCH][ARM]Use ACLE compiler macros for determining the available features

[Richard Earnshaw <rearnsha at arm dot com>]

GCC has for a number of years provides a set of pre-defined macros for
use with determining the ISA and features of the target during
pre-processing.  However, the design was always somewhat cumbersome in
that each new architecture revision created a new define and then
removed the previous one.  This meant that it was necessary to keep
updating the support code simply to recognise a new architecture being
added.

The ACLE specification
(http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.set.swdev/index.html)
provides a much more suitable interface and GCC has supported this since
gcc-4.8.

This patch makes use of the ACLE pre-defines to map to the internal
feature definitions.  To support older versions of GCC a compatibility
header is provided that maps the traditional pre-defines onto the new
ACLE ones.

Long term we may want to retire the internal pre-defines and move to
using the ACLE features directly; but that's for another day.

I'll commit this in ~24 hours if I don't hear any objections.

R.

	* libc/machine/arm/acle-compat.h: New file.
	* libc/machine/arm/arm_asm.h: Use it.

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