BUG #18200: Undefined behaviour in interval_div

The following bug has been logged on the website:

Bug reference: 18200
Logged by: Alexander Lakhin
Email address: exclusion(at)gmail(dot)com
PostgreSQL version: 16.1
Operating system: Ubuntu 22.04
Description:

The following query:
SELECT interval '12000000 months' / 0.001;

triggers an ubsan-detected error:
timestamp.c:3408:18: runtime error: 1.2e+10 is outside the range of
representable values of type 'int'

Without ubsan the result is:
-178956970 years -8 mons -2562047788:00:54.775808

This bogus value returned on REL_15_STABLE .. master, but on e39f99046~1
I get:
ERROR: interval out of range

without ubsan. Though with the sanitizer I see the same complaint (and it
can be seen on previous branches including REL_12_STABLE):
timestamp.c:3318:18: runtime error: 1.2e+10 is outside the range of
representable values of type 'int'