This patch backports the changes made to strengthen the barriers emitted for
the __sync compare-and-swap builtins.

The trunk patch submission is at
https://gcc.gnu.org/ml/gcc-patches/2015-06/msg01411.html
The commit is at https://gcc.gnu.org/ml/gcc-cvs/2015-06/msg01236.html

Tested the series for arm-none-linux-gnueabihf with check-gcc

Ok for the branch?
Matthew

2015-07-02  Matthew Wahab  <matthew.wahab@arm.com>

	Backport from trunk:
	2015-06-29  Matthew Wahab  <matthew.wahab@arm.com>

	PR target/65697
	* config/armc/arm.c (arm_split_compare_and_swap): For ARMv8,
	replace an initial acquire barrier with final barrier.