This change uses the Arm v8.3 pointer authentication instructions in
order to protect return addresses stored on the stack.  The generated
code signs the return address before storing on the stack and
authenticates it after loading it. This also changes the stack frame
iterator in order to authenticate stored return addresses and re-sign
them when needed, as well as the deoptimizer in order to sign saved
return addresses when creating new frames. This offers a level of
protection against ROP attacks.

This functionality is enabled with the v8_control_flow_integrity flag
that this CL introduces.

The code size effect of this change is small for Octane (up to 2% in
some cases but mostly much lower) and negligible for larger benchmarks,
however code size measurements are rather noisy. The performance impact
on current cores (where the instructions are NOPs) is single digit,
around 1-2% for ARES-6 and Octane, and tends to be smaller for big
cores than for little cores.

Bug: v8:10026
Change-Id: I0081f3938c56e2f24d8227e4640032749f4f8368
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1373782
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66239}