Re: Update Windows binaries

[Vasily Galkin <galkin-vv yandex ru>]

Hello again!
Due to recent pangocairo changes in mingw-msys2 meld 3-18 become incompatible with it (even running from 
checkout).
So I cherrypicked last changes Keegan Witt made for 3-18 (thanks!) changes to new branch created from current 
master, fix pangocairo and make some more adjustments:
 - fixed paths to glib data installation
 - XDG_DATA_DIR separator
 - added caching of msys packages in appveyour data to achieve build stability on rolling-release msys2
 - remove libwebp (it looks unused?)
 - unified. renamed mingw64+32 scripts in single msys2 script

The repo with scripts is here - 
https://gitlab.gnome.org/galkinvv/meld/commits/65f5c2fe1d4564a40fb47247a996eff6417ff74d
(meld-installer-build branch)
The resulting installer is here:
https://ci.appveyor.com/project/galkinvv/meld-ljlj2/build/job/jja76xhc0qxdq461/artifacts

This installer installs meld master (3.19-based) and the resulting installation behaviour is identical to 
meld executed from checkout on msys2:
 - It mostly works if executed from cmd line with files arguments (works 80% of time, but may crash or hang)
 - for up-to-date msys2 version meld master has huge problems with selection&comparing files via new tab 
page, at least on windows 7.

So it looks that installation build scripts themselves are mostly correct and this version achieves basic 
windows compatibility for current master with msys2.
The commit history of achieving this compatibility mostly contains trial&error commits.
Should the commit history be included in merge request or squashed to single commit describing ideas of most 
important changes?

Note for those reading this message in search of recent meld windows binaries: the installer linked above 
installs the very unstable combination of meld with recent msys2 (with known interoperability bugs).
There exists much more stable 3.18-based installer linked in 
https://mail.gnome.org/archives/meld-list/2018-April/msg00019.html

> Ah. Thanks Vasily! I pushed some more changes, both builds are producing an msi now. Unfortunately, both 
> are also still producing the error
>
> Microsoft Visual C++ Runtime Library
> Runtime Error!
> Program: C:Program Files (x86)MeldMeld.exe
> This application has requested the Runtime to terminate it in
> an unusual way
> Please contact the application's support team for more
> information.
>
> I'm wondering why I'm getting a Visual C++ error, if these are mingw. I think I've still got some wires 
> crossed somewhere.