gdbstub/user: rename and use bool for running_state This is just a clean-up to document what we using the running variable for in user-mode. Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-ID: <20260203115201.2387721-12-alex.bennee@linaro.org> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>