StackGuard::HandleInterrupts used to take a lock for testing and
clearing each individual interrupt bit. This CL changes that to a
single read up front.

Slight behavioral changes:

1. A TERMINATE_EXECUTION interrupt is now handled first; we
immediately exit and preserve all other interrupts (in case V8 is
later resumed).
2. Since interrupts are read once, it is no longer possible to request
an interrupt *within* HandleInterrupts that will later be processed
within the same HandleInterrupts call.
3. Stack limits are reset immediately after reading the interrupt
bits, and prior to actually processing the interrupts.

Bug: v8:9328
Change-Id: I3048bb413213d11307df49e0014b64a2b43444e0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1653115
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62132}