Nevertheless I did not modified the qt sources and builds were working fine after compilation for Linux 32 bits and QNX, I just had to add QtWebKit from the community release because it is not a part of official release anymore.
Actually for QtWebkit on QNX, the app seems have found the module but not the proper version (3.0). For Virtual Keyboard I did nothing more than compiling and try to use the exemple provided with Qt sources, first on Linux 32 bits then on my QNX arm v7 target. I did that with several others QML examples also provided with Qt sources and I did not encounter that kind of behaviour, no other modules where missing.
Maybe i missed something on my target configuration (libs install, Path, ...), I just would like to know if there is a way to list which modules and version are properly installed on a specific system (Linux, QNX).
No problems as such, but a launcher application named Start was perhaps not compatible with Android 6 and managed to make my app lose texts on pushbuttons... That application was not updated when the OS was updated and the mechanism how it managed to do mess up another app is unclear... (Of course it can be that Qt 5.6 has a deficiency that makes it vulnerable to environmental issues in Marshmallow.)
@krzaq I'm surprised anything changed at all with the c++14 flag. Are you using 5.6.0-rc ? In my caseCONFIG += c++11 c++14 doesn't seem to do anything at all when compiling to Android. I'm using 5.6.0-rc and with CONFIG += c++11 c++14 I'm just getting -std=c++11.
With Qt 5.5.1 CONFIG += c++11 c++14 I get -std=c++1y added to the mix and I can use relevant functionality (std::make_unique).