Most of the Makefile bits are obsolete and can be removed.
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
We do not need to ask cmake for the dependencies, so just use the
pkg-config mechanism. Keep "auto" for SDL so that it tries using
sdl-config too.
The documentation is adjusted to use SDL2_image as the example,
rather than SDL which does not use the "pkg-config" method.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>