port-vax/59265: t_strtod:strtod_hex test is failing

[campbell+netbsd%mumble.net@localhost]

>Number:         59265
>Category:       port-vax
>Synopsis:       t_strtod:strtod_hex test is failing
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-vax-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Apr 07 00:55:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The StrtoBSD Vaxination
>Environment:
>Description:
*** Check failed: /tmp/build/2025.04.04.21.52.19-vax/src/tests/lib/libc/stdlib/t_strtod.c:123: end != str + 4: str=0x1190a end=0x1190c
*** Check failed: /tmp/build/2025.04.04.21.52.19-vax/src/tests/lib/libc/stdlib/t_strtod.c:124: d=0=0x0p+0 signbit=0
*** Check failed: /tmp/build/2025.04.04.21.52.19-vax/src/tests/lib/libc/stdlib/t_strtod.c:132: d=0=0x0p+0 signbit=0

https://releng.netbsd.org/b5reports/vax/2025/2025.04.04.21.52.19/test.html#lib_libc_stdlib_t_strtod_strtod_hex

Not sure why strtod is only consuming `-0' and ignoring `x0'.

The sign bit tests are failing because VAX floating-point doesn't have signed zeroes.
>How-To-Repeat:
cd /usr/tests/lib/libc/stdlib
atf-run t_strtod | atf-report
>Fix:
1. Not sure how to fix the first problem, that it consumes only `-0' and not the following `x0'.
2. Conditionalize the signbit tests on whether the machine has signed zeroes.  Or maybe write them as: signbit(d) == signbit(-0.)