ptsname_r: Work around ptsname_r bug on NetBSD 10.0. * m4/ptsname_r.m4 (gl_FUNC_PTSNAME_R): On NetBSD, arrange to override ptsname_r. * lib/ptsname_r.c (ptsname_r): Add workaround for NetBSD bug. * doc/glibc-functions/ptsname_r.texi: Mention the NetBSD bug.