[Development] MinGW-builds in CI system (Qt 5)

[Koehne Kai]

Hi Janne and Samuli,

Now that the big thing (CI system migration) is done, I'm wondering whether we can get also MinGW into the CI system for Qt 5? It's a Tier 1 platform, so it should really be part of the CI testing. I understand that in the past we didn't do it because the outdated gcc in Mingw caused quite some headache (crashed), but things have improved since then. It's also a somewhat slow platform (mingw32-make -j has still it's quirks because sometimes the debug and release rules touch the same file), but until we fixed that I could imagine we run it e.g. without tests ...

The MinGW distribution we've tested best so far is MinGW-builds: 
http://sourceforge.net/projects/mingwbuilds

MinGW-builds is featuring both a 32 bit and 64 bit compiler package, and ideally we should test both.
 
Regards

Kai