plugin: Don't warn on copy constructors on dllexported classes.
In general, implicit constructors are generated on demand. But
in the Windows component build, dllexport causes instantiation of
the copy constructor which means that this fires on many more
classes. For now, suppress this on dllexported classes.
(This does mean that windows component builds will not emit this
warning in some cases where it is emitted in other configs, but
that's the better tradeoff at this point).
BUG=483986,467288
R=hans@chromium.org
Review URL: https://codereview.chromium.org/
1129843005
Cr-Commit-Position: refs/heads/master@{#329036}