Use short timezone names in _tzset_js

[sbc100]

Without this change then timezone names will be the long form (Pacific
Standard Time) rather than the short form (PST), and since TZNAME_MAX
in musl is 6 (same in POSIX) the long names were getting truncated.

Fixes: #21582

[jrobichaux]

sorry to jump in here, but on the call to:

date.toLocaleTimeString(undefined, {timeZoneName:'short'}).split(' ')[2];

that works properly for me with English US settings (returns "EDT"), but if I change to English UK it returns "undefined" because it's a 24-hour clock (no AM/PM in the string).

[sbc100]

sorry to jump in here, but on the call to:

date.toLocaleTimeString(undefined, {timeZoneName:'short'}).split(' ')[2];

that works properly for me with English US settings (returns "EDT"), but if I change to English UK it returns "undefined" because it's a 24-hour clock (no AM/PM in the string).

What does date.toLocaleTimeString(undefined, {timeZoneName:'short'}) return in this case?

Should I pass en.us as the first argument here to force English US maybe?

[jrobichaux]

With my regional settings on English UK the call to date.toLocaleTimeString(undefined, {timeZoneName:'short'}) returns e.g. "11:55:09 GMT-4" using Edge on Windows 10.

If I change the call to date.toLocaleTimeString('en-US', {timeZoneName:'short'}) it returns e.g. "11:59:21 AM EDT" which is what you're looking for, but I have no idea if en-US is available for all browsers in all languages.

[sbc100]

I opened #21596 to fix this issue and add more testing.