doc: Fix the previous commit. Suggested by Bruno Haible in: <https://lists.gnu.org/archive/html/bug-gnulib/2024-12/msg00236.html>. * doc/posix-functions/getservbyname.texi: Mention the Windows declaration under "Portability problems fixed by Gnulib". * doc/posix-functions/getservbyport.texi: Likewise.