QEMU adds the path to glib.h to all compilation commands.  This is simpler
due to the pervasive use of static_library, and was grandfathered in from
the previous Make-based build system.  Until Meson 0.63 the only way to
do this was to detect glib in configure and use add_project_arguments,
but now it is possible to use add_project_dependencies instead.

gmodule is detected in a separate variable, with export enabled for
modules and disabled for plugin.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>