Fix i386 crash at Qt startup and make Qt configuration 32bit aware

Several things in this pull request:
* Qt project files should now correctly choose ffmpeg libs and includes for ```x86``` and ```x86_64```. I've updated only the linux config as I'm compiling only under linux and I don't have a 32bit Windows installation at my disposal.
* Old ```__cpuid()``` got removed because it was generating a strange assembly on ```i386``` which resulted in a total destruction of ```PIC``` and eventually a segfault.  The ```__cpuidex()``` works fine (xref: #4233) and with ```excval==0``` it does the same job as the old ```__cpuid()``` so I have refactored it a bit to be used in whole the ```CPUDetect.cpp```.
* There was some stray code bug in Qt window code due to the change of a function name.