The problem were missing V8_EXPORT_PRIVATE and V8_EXPORT.

The unittests test if the trap handler only handles those traps it
is supposed to handle:
* Only handle traps when the thread-in-wasm flag is set.
* Only handle traps of the right type, i.e. memory access violations.
* Only handle traps at recorded instructions.

The tests also test the consistency of the thread-in-wasm flag. I made
one change in the trap handler where that consistency could be
violated.

All tests are executed with the default trap handler provided by V8,
and with the trap handler callback installed in a test signal/exception
handler.

Patchset 1 is the original CL.

R=mstarzinger@chromium.org

Change-Id: I172d94f24cdba4c3a1f7f344825b059dbb59da79
Reviewed-on: https://chromium-review.googlesource.com/c/1351024Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57947}