closefrom: add NetBSD, OpenBSD, DragonflyBSD

NetBSD, OpenBSD and DragonFly return c_int, FreeBSD returns void,
so we can't just add it in freebsdlike.
Apple doesn't seem to support closefrom at all at this point.

(backport <#4290>)
(cherry picked from commit 8512ab4)

Author: tobhe

libc-test/semver/dragonfly.txt

@@ -1296,6 +1296,7 @@ clock_getcpuclockid
 clock_getres
 clock_nanosleep
 clock_settime
+closefrom
 cmsgcred
 cmsghdr
 cpuctl_cpuid_args_t

libc-test/semver/netbsd.txt

@@ -1252,6 +1252,7 @@ clearerr
 clock_getres
 clock_nanosleep
 clock_settime
+closefrom
 cmsghdr
 consttime_memequal
 daemon

libc-test/semver/openbsd.txt

@@ -1068,6 +1068,7 @@ chroot
 clearerr
 clock_getres
 clock_settime
+closefrom
 cmsghdr
 daemon
 devname

src/unix/bsd/freebsdlike/dragonfly/mod.rs

@@ -1702,6 +1702,8 @@ extern "C" {
         mntvbufp: *mut *mut crate::statvfs,
         flags: c_int,
     ) -> c_int;
+
+    pub fn closefrom(lowfd: c_int) -> c_int;
 }
 
 #[link(name = "rt")]

src/unix/bsd/netbsdlike/mod.rs

@@ -861,6 +861,8 @@ extern "C" {
         flags: c_int,
         timeout: *mut crate::timespec,
     ) -> c_int;
+
+    pub fn closefrom(lowfd: c_int) -> c_int;
 }
 
 cfg_if! {