ARMv8.1 adds instructions for atomic compare-and-swap with optional
memory ordering specifiers. This patch series adds the instructions to
GCC, making them available with -march=armv8.1-a or with
-march=armv8-a+lse, and using them to implement the __sync and __atomic
builtins.

This patch adds an internal TARGET_LSE macro, to check target support
for the atomic instructions.

Subsequent patches
- add and use atomic compare-and-swap instructions;
- add tests for the compare-and-swap;

Tested the series for aarch64-none-linux-gnu with native bootstrap and make
check and for aarch64-none-elf with cross-compiled check-gcc. Also tested
aarch64-none-elf with cross-compiled check-gcc on an emulator that supports
ARMv8.1.

Ok for trunk?
Matthew

2015-08-12  Matthew Wahab  <matthew.wahab@arm.com>

	* config/aarch64/aarch64.h (AARCH64_ISA_LSE): New.
	(TARGET_LSE): New.