The F: patterns in the "GDB stub" section forgot gdbstub.h; add it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210208113729.25170-1-peter.maydell@linaro.org>
Message-Id: <20210211122750.22645-10-alex.bennee@linaro.org>