AArch64 - disable CB[N]Z TB[N]Z when tracking speculation

AArch64 - disable CB[N]Z TB[N]Z when tracking speculation

The CB[N]Z and TB[N]Z instructions do not expose the comparison through
the condition code flags.  This makes it impossible to track speculative
execution through such a branch.  We can handle this relatively easily
by simply disabling the patterns in this case.

A side effect of this is that the split patterns for the atomic operations
need to also avoid generating these instructions.  They mostly have simple
fall-backs for this already.

	* config/aarch64/aarch64.md (cb<optab><mode>1): Disable when
	aarch64_track_speculation is true.
	(tb<optab><mode>1): Likewise.
	* config/aarch64/aarch64.c (aarch64_split_compare_regs): Do not
	generate CB[N]Z when tracking speculation.
	(aarch64_split_compare_and_swap): Likewise.
	(aarch64_split_atomic_op): Likewise.

(backported eaf891585b16ef84046ae73a01bb1c7189c682e9)

Change-Id: I0d0a090ef7bcf074b9e4d6ee115e71faa157962f
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@263172 138bc75d-0d04-0410-961f-82ee72b054a4