Jolla's SailfishOS SDK was released quite some time back for Linux, OSX and Windows. I had tried it once during that time but only compiled some sample apps until I found some time recently to port one of my N9/Harmattan apps to Sailfish/Nemo.
The app needed to use the device's GPS system to know its coordinates for which I used QtMobility's location API. However, when trying to compile, the SDK wasn't able to find the QGeoPositionInfoSource header and I found that it was really missing from the SDK's include dir. In fact, the whole QtMobility module was missing.
SailfishOS SDK doesn't contain QtMobility by default, you have to install it manually. Luckily the SailfishOS SDK control center makes it easy.