Set Qt to build debug menus on non Linux platforms and fix some debugger crashes

This makes Common.pro and Native.pro use their own distinct object directories
to prevent the two fbo.cpp and sha1.c files repectively to clash into the same
*.obj file.

The registerlist had polled register values of -1 in some cases when resizing
the window. Making sure it doesn't poll values smaller than 0 fixes it.

The memoryview crashed if it was switched into symbol mode outside of the
symbol definition range. Also, under Windows the monospace font wasn't
used because there's not literal font called "monospace" so a font family
hint had to be used.

The UpdateDisassembly() function jumped to the current PC, which sounds
reasonable at first but the issue is that this function gets called when a
breakpoint get set, so if you set a breakpoint somewhere completely
different then you suddenly lose that position for no good reason.

Enable the desktop QT interface for all non ARM QT platforms