lib/59341: _longjmp(..., 0) makes _setjmp return zero

[campbell+netbsd%mumble.net@localhost]

>Number:         59341
>Category:       lib
>Synopsis:       _longjmp(..., 0) makes _setjmp return zero
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Apr 22 12:45:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The _LongBSD Foundazero
>Environment:
>Description:
On mips, _longjmp doesn't force the argument to be nonzero, so tests/lib/libc/setjmp/t_setjmp:_longjmp_zero fails.

The same problem has plagued kernel setjmp/longjmp and I filed too many MD PRs for that, so let's just keep one PR here and a checklist for an audit:

[ ] aarch64
[ ] alpha
[ ] arm
[ ] hppa
[ ] i386
[ ] ia64
[ ] m68k
[ ] mips
[ ] or1k
[ ] powerpc
[ ] powerpc64
[ ] riscv
[ ] sh3
[ ] sparc
[ ] sparc64
[ ] vax
[ ] x86_64
>How-To-Repeat:
cd /usr/tests/lib/libc/setjmp
atf-run t_setjmp | atf-report
>Fix:
Yes, please!