Without this, and additional SIGINT while waiting for the next statement
(e.g. during `time.sleep`) will stop at `sigint_handler`.

With this patch:

    > …/t-pdb-sigint-in-sleep.py(10)<module>()
    -> sleep()
    (Pdb) c
    ^C
    Program interrupted. (Use 'cont' to resume).
    ^CKeyboardInterrupt
    > …/t-pdb-sigint-in-sleep.py(6)sleep()
    -> time.sleep(10)
    (Pdb)

Without this patch:

    > …/t-pdb-sigint-in-sleep.py(10)<module>()
    -> sleep()
    (Pdb) c
    ^C
    Program interrupted. (Use 'cont' to resume).
    ^C--Call--
    > …/cpython/Lib/pdb.py(188)sigint_handler()
    -> def sigint_handler(self, signum, frame):
    (Pdb)

This was changed / regressed in https://github.com/python/cpython/commit/10e54aeaa234f2806b367c66e3fb4ac6568b39f6 (3.5.3rc1?), when it was moved while fixing issue 20766.