toolchain/58959: tools pax: implicit declaration of ffs

[campbell+netbsd%mumble.net@localhost]

>Number:         58959
>Category:       toolchain
>Synopsis:       tools pax: implicit declaration of ffs
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Jan 04 07:15:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        10/9
>Organization:
The PaxBSD Ffoundations
>Environment:
>Description:
Building netbsd-10 on a netbsd-9 userland gives this warning:

/usr/src/10/tools/pax/../../bin/pax/options.c: In function 'printflg':
/usr/src/10/tools/pax/../../bin/pax/options.c:1890:16: warning: implicit declaration of function 'ffs' [-Wimplicit-function-declaration]
  while ((nxt = ffs(flg)) != 0) {
                ^~~

The build succeeds but the warning is alarming, may become a compiler error later, and could risk miscompilation.
>How-To-Repeat:
build netbsd-10/aarch64 on a netbsd-9/amd64 userland
>Fix:
Yes, please!