On other OSes, it's not possible to have qmake or the qt5 pkg-config
files and not have moc, and `moc` will not be in `PATH`, so this only
causes problems.
Needs gnustl for C++ STL support, which is the GNU STL on Android API
19 and older, and is a wrapper for the llvm-libc++ STL on newer APIs.
QtGui C++ templates use GL functions, so GLESv2 is needed at link time
The android code path is slightly different than the EGLFS one,
so I added previously a HAVE_QT_ANDROID define for use with qmake.
Here I also add it in meson, although I expect nobody will ever use
meson to build this, as it's complicated.
Tested on linux with X11/wayland and semi-tested on Windows.
Windows crashes on item destruction however this is better than nothing.
Fix up some win32 build issues on the way with mismatched {} and
G_STMT_{START,END}
