ast.c: fstring_fix_node_location() downcasts a pointer difference to
a C int. Replace int with Py_ssize_t to fix the compiler warning.

(cherry picked from commit fb7e799)

(cherry picked from commit 028f0ef)

Use the _PyTime_t type and round away from zero (ROUND_UP,
_PyTime_ROUND_TIMEOUT) the sleep duration, when converting a Python
object to seconds and then to milliseconds. Raise an OverflowError in
case of overflow.

Previously the (int)double conversion rounded towards zero
(ROUND_DOWN).

(cherry picked from commit ca40501)