Fixed Qt5 and Linux builds

[Wohlstand]

I tested this at me, it works flawlessly! I use Linux Mint 19.3.

Note: I had to use the -no-pie flag that makes executable being working from the file managers (that need for GCC 6 and newer, GCC 5 and older, and CLang has no this mess). If you'll try to build with CLang or an older GCC version the error may appear. Please verify the build on Qt 4 if you still support it. I had to port the entire project into Qt 5.