c_entry_fp is normally cleared in `LeaveExitFrame`, but we adjust
the frame without it in the exception path.

This can cause the SafeStackFrameIterator to assume we have an exit
frame and iterate over frames incorrectly, which for arm64 can
cause pointer authentication failures with CFI enabled. Even without
the pointer authentication failure, we iterate over frames incorrectly,
so make this change for other architectures too.

Also clear c_entry_fp in the beginning of JSEntry, after pushing it
on the stack. Not doing this doesn't cause pointer authentication
failures, but it will make the SafeStackFrameIterator assume we
are executing C++ and miss the JS frames on top.

Bug: v8:10026
Change-Id: Ie94834920f51e9f1cc5c1c775596726b61fc0507
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2642256Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/master@{#72458}