Support new and discontinue old compilers

[David Ostrovsky]

I'm pleased to share with you, that MSVC 15 (aka VS 2017) is up
and running on master: [1].

After fixing the VC++ runtime merge module merging problem in resulted
MSI in MSVC 14.0 and MSVC 15.0, the produced MSI can not only be
installed, but the LO can actually run after the installation. The VC++
Runtime merge module merging bug that started to show up since MSVC
14.0, is appeared to be a trivial problem, that was surprisingly hard
to track down: [2]. I don't want to enter into glory details here as
for why that was the case, but I will write a blog about that one.

That raises the question, if we are ready to move forward and left MSVC
12.0 (aka VS 2013) behind us: [3]. I know, it's always hard to get a
feedback on such questions, as you can see no reaction on this infra
issue: [4]. Needless to say that I asked on IRC too, without any
response, so I guess the only way to get a feedback on that one, is to
merge that change and see, if it's going to be reverted...

* [1] https://gerrit.libreoffice.org/#/c/31279
* [2] https://gerrit.libreoffice.org/#/c/33366/
* [3] https://gerrit.libreoffice.org/#/c/22588/
* [4] https://redmine.documentfoundation.org/issues/2147