Resolve X11/Xlib.h define of Bool and Qt5 (5.2)

Xlib.h has a "#define Bool int", which causes compilation issues with other uses of
Bool, specifically in qsonvalue.h in Qt5.  This patch rearranges the MythTV source file
includes to bypass the issue.

Fixes #12065
Signed-off-by: Stuart Auchterlonie <stuarta@squashedfrog.net>

Signed-off-by: Stuart Auchterlonie <stuarta@mythtv.org>
Remove check_cxxflags which doesn't work
Fix mythnetvision.pro for Qt5
Enable compilation of a couple of files that were disabled on Qt5 because they are apparently not compatible. They build, so let them.