The current update MSVC 2017.5 supports fancy new C++ features, but
unfortunately in its default C++14 mode it falls over and dies with
an internal compiler error as soon as it sees the WeakImplHelper
variadic template.

In order to work around the ICE, build everything as C++17,
which somehow doesn't crash.

This causes loads of deprecation warnings about obsolete std::this
and badly designed std::that, almost all of them from boost headers,
which are well known for following every best practice in the C++ book.

Liberally sprinkle macros around to suppress the warnings for now,
like we already do with the other million warnings from boost headers.

Change-Id: Ia6b6ef5e457b5fe3c8cfe361ba5da39376bb7c4c
Reviewed-on: https://gerrit.libreoffice.org/48225Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>