[Development] Supported platforms for Qt 5.8

[Knoll Lars]

Hi,

Now that 5.7 is branched, I'd like to propose that we update our list of supported compilers and platforms for Qt 5.8. After some discussions with different people, here's an initial proposal from my side:

* We drop support for VS2012. This implicitly drops support for WEC2013. Reason is that the compiler is still having rather large problems with it's C++11 support. I hope that we could serve the WEC market rather well with 5.6 and 5.7 for the years to come. In the end, the benefit we get with dropping the compiler will hopefully outweigh the cost (loosing WEC) by a good margin.

* We drop support for Vista. Vista has a market share that is below 2%, and again we have 5.6 to cover that platform for the next 3 years.

* We should upgrade MingW to a newer version, possibly based on gcc 5.2

* No changes for Windows Phone, we continue to support 8.1 and 10.

* We require the latest Xcode toolchain and OS X on the Mac for compiling (see separate mailing list thread). We support deployment to OS X 10.9 and later (dropping 10.8)

* On iOS, we also require the latest Xcode toolchain for compiling. We continue with iOS 7 as the minimum supported version for deployment.

* Minimum version for Android is probably going to stay with 4.1 (as with 5.7). We would like to add a 64 bit build to the CI

* We continue to support QNX 6.6

* On Linux, we will investigate upgrading our packaging machine from RHEL 6.6 to RHEL 7. We should also try to update our Ubuntu CI machines to 16.04 once it's released.


Let me know if you see larger problems with these changes.

Cheers,
Lars