NetBSD: add ptsname_r support

(backport <#4608>)
(cherry picked from commit e634372)

Author: 0-wiz-0

src/unix/bsd/netbsdlike/netbsd/mod.rs

@@ -2497,6 +2497,8 @@ extern "C" {
         winp: *mut crate::winsize,
     ) -> crate::pid_t;
 
+    pub fn ptsname_r(fd: c_int, buf: *mut c_char, buflen: size_t) -> c_int;
+
     #[link_name = "__lutimes50"]
     pub fn lutimes(file: *const c_char, times: *const crate::timeval) -> c_int;
     #[link_name = "__gettimeofday50"]