Baseline bump to MSVC 2015 Update 3

[David Ostrovsky]

On Thu Mar 2 16:02:30 UTC 2017 Stephan Bergmann wrote:

>As has been brewing for some time and just got accepted in today's ESC
>meeting, we'll bump master (towards LO 5.4) to MSVC 2015 Update 3 as 
>basline for MSVC builds on Windows.

Thanks!

>* The wiki developer documentation will likely need updating.  Any 
>volunteers?

Done.

>* Noteworthy improvements this brings to us regarding C++11-and-beyond
>support is that HAVE_CXX11_CONSTEXPR and HAVE_UTF16_STRING_LITERAL 
>should now always be true.

I would also add python de-duplication and shipping the same python
version 3.5.3 on all platforms (duplication was needed, as Python 3.5.x
abandoned support for msvc 2013 and only supported msvc 2015).

It worth also noting that there is substantial performance benefit for
debug build, once /debug:fastlink support CL is merged: [1].

* [1] https://gerrit.libreoffice.org/34330