The functions itoa() and utoa() are non-standard, not exported by Cygwin 
and also unavailable on FreeBSD and Linux (glibc and musl libc). Busybox 
for example could not be build OOTB using newlib's stdlib.h because 
there are conflicts with local functions with same names but different 
signatures.

See the original posts on the Cygwin list for more details:
https://sourceware.org/pipermail/cygwin/2024-January/255216.html
https://sourceware.org/pipermail/cygwin/2024-January/255217.html

Corinna proposed to either drop these functions entirely or hide the 
prototypes on Cygwin only. I attached a patch for the second alternative.

-- 
Regards,
Christian