Switch to using the arandom sysctl on NetBSD (same as FreeBSD).

Rename it from freebsd.rs to sysctl_arandom.rs.

NetBSD has been patching rustc for some time to use the FreeBSD
implementation because every single invocation of the compiler
may drain from the entropy pool and cause the next to block.

This can massively inflate build times for rust sofware, or cause
it to fail entirely, especially in VMs (for example, our Xen package
building cluster).

src/lib.rs

@@ -198,7 +198,7 @@ cfg_if! {
     } else if #[cfg(target_os = "emscripten")] {
         #[path = "use_file.rs"] mod imp;
     } else if #[cfg(target_os = "freebsd")] {
-        #[path = "freebsd.rs"] mod imp;
+        #[path = "sysctl_arandom.rs"] mod imp;
     } else if #[cfg(target_os = "fuchsia")] {
         #[path = "fuchsia.rs"] mod imp;
     } else if #[cfg(target_os = "haiku")] {
@@ -212,7 +212,7 @@ cfg_if! {
     } else if #[cfg(target_os = "macos")] {
         #[path = "macos.rs"] mod imp;
     } else if #[cfg(target_os = "netbsd")] {
-        #[path = "use_file.rs"] mod imp;
+        #[path = "sysctl_arandom.rs"] mod imp;
     } else if #[cfg(target_os = "openbsd")] {
         #[path = "openbsd.rs"] mod imp;
     } else if #[cfg(target_os = "redox")] {

src/freebsd.rs → src/sysctl_arandom.rs

@@ -6,7 +6,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! Implementation for FreeBSD
+//! Implementation for FreeBSD and NetBSD
 use crate::util_libc::{sys_fill_exact, Weak};
 use crate::Error;
 use core::{mem, ptr};
@@ -27,7 +27,7 @@ fn kern_arnd(buf: &mut [u8]) -> libc::ssize_t {
         )
     };
     if ret == -1 {
-        error!("freebsd: kern.arandom syscall failed");
+        error!("sysctl_arandom: kern.arandom syscall failed");
         -1
     } else {
         len as libc::ssize_t