Correct version getter for QMake build

[szszszsz]

Add get_major_library_version and similar symbols to QMake build.
Nitrokey App build done via QMake fails currently.

Connected: #117

[robinkrahl]

It is also possible to define a new compiler that just runs sed to replace the placeholders in version.cc.in. See the Advanced Usage: Adding Compilers section in the qmake manual.

You can find an example implementation on my qmake-version branch. I’m just not sure whether you expect qmake to run on Windows and whether we can rely on sed being available.

[szszszsz]

Temporarily fixed via constants with cdd155e