MSVC 2015 and 2017 implement std::is_trivially_copyable, but not
correctly. Hence, reimplement it using more low-level primitives.

For stdlibc++ versions below 5.0, we already have a workaround for the
missing support of std::is_trivially_copyable, but this is an unsound
approximation, because it is ignoring move constructor, move assignment
and copy assignment. Therefore, do not use this approximation for
asserting trivial copyability of a type.

Finally, add unittests for the new is_trivially_copyable
implementations.

R=mstarzinger@chromium.org
CC=loorongjie@gmail.com

Change-Id: I9ee56a65882e8c94b72c9a2d484edd27963a5d89
Reviewed-on: https://chromium-review.googlesource.com/941521Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51651}