Close #14180: Factorize code to convert a number of seconds to time_t, timeval or timespec

time.ctime(), gmtime(), time.localtime(), datetime.date.fromtimestamp(),
datetime.datetime.fromtimestamp() and datetime.datetime.utcfromtimestamp() now
raises an OverflowError, instead of a ValueError, if the timestamp does not fit
in time_t.

datetime.datetime.fromtimestamp() and datetime.datetime.utcfromtimestamp() now
round microseconds towards zero instead of rounding to nearest with ties going
away from zero.
diff --git a/Include/pytime.h b/Include/pytime.h
index 2ea64c9..0473dc7 100644
--- a/Include/pytime.h
+++ b/Include/pytime.h
@@ -39,9 +39,22 @@
      (tv_end.tv_usec - tv_start.tv_usec) * 0.000001)
 
 #ifndef Py_LIMITED_API
+/* Convert a number of seconds, int or float, to time_t. */
+PyAPI_FUNC(int) _PyTime_ObjectToTime_t(
+    PyObject *obj,
+    time_t *sec);
+
+/* Convert a number of seconds, int or float, to a timeval structure.
+   usec is in the range [0; 999999] and rounded towards zero.
+   For example, -1.2 is converted to (-2, 800000). */
+PyAPI_FUNC(int) _PyTime_ObjectToTimeval(
+    PyObject *obj,
+    time_t *sec,
+    long *usec);
+
 /* Convert a number of seconds, int or float, to a timespec structure.
-   nsec is always in the range [0; 999999999]. For example, -1.2 is converted
-   to (-2, 800000000). */
+   nsec is in the range [0; 999999999] and rounded towards zero.
+   For example, -1.2 is converted to (-2, 800000000). */
 PyAPI_FUNC(int) _PyTime_ObjectToTimespec(
     PyObject *obj,
     time_t *sec,
diff --git a/Include/timefuncs.h b/Include/timefuncs.h
deleted file mode 100644
index 3c43575..0000000
--- a/Include/timefuncs.h
+++ /dev/null
@@ -1,25 +0,0 @@
-/*  timefuncs.h
- */
-
-/* Utility function related to timemodule.c. */
-
-#ifndef TIMEFUNCS_H
-#define TIMEFUNCS_H
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-
-/* Cast double x to time_t, but raise ValueError if x is too large
- * to fit in a time_t.  ValueError is set on return iff the return
- * value is (time_t)-1 and PyErr_Occurred().
- */
-#ifndef Py_LIMITED_API
-PyAPI_FUNC(time_t) _PyTime_DoubleToTimet(double x);
-#endif
-
-
-#ifdef __cplusplus
-}
-#endif
-#endif  /* TIMEFUNCS_H */