Investigating GNU ld, I learned that there is no easy way (~= no way) to suppress the warnings (other than 2>/dev/null). It was implemented by the special section named gnu.warning.SYM where SYM is a symbol. I think that this is not-so-good for glibc to notify its users about possible static link problem, by gnu.warning.SYM.

I found two issues in libgpg-error for spawning functions.

POSIX documentation never says that PSHARED=0 prevents sharing among processes. In my opinion, it still conforms to POSIX even when a PSHARED=0 semaphore can be shared between parent and child processes.

I've tried the new patch in my environment, and it fixes the gnupg HEAD self tests as well. Thank you!

In tests/migrations, (unlike tests/openpgp and tests/cms), the tests do not prepare gpg-agent, but it is gpg which invokes gpg-agent if needed.
Because of that, on NetBSD (where POSIX semaphore has a different semantics), it hangs with gpg --list-secret-key, when gpg tries to spawn the gpg-agent process.
In the old code of 2.4, it simply ignore the npth_protect and npth_unprotect when calling fork to spawn a process.
New code in libgpg-error cares about npth_protect and npth_unprotect but it was not sufficient; We need to care about NetBSD's semantics. Child process should not call npth_protect. With shared semantics, child process's calling npth_protect affects to cause parent process: it hangs.

TL;DR
This ticket was created because building static-linked gpgv shows warnings from glibc for getpwnam and getpwuid.
Basically, we can/should ignore the warnings from glibc at link time (for normal use cases), because it is irrelevant.

Let us mark this as a feature requests. gepwnam(3) is a standard libc function and if glibc does not support it; this is more likely a glibc bug than a bug in an application.

It seems this broke the self tests (and gpgme, and notmuch) on NetBSD: https://dev.gnupg.org/T8065

I think we won't fix that for 2.2