Fix build and tests issues on OpenBSD 6.4+

1)  lutimes doesn't exist on OpenBSD so it needs to be under conditional
    compilation.

    The only "reference" that I could find related to this is the discussion
    here: https://github.com/rust-lang/libc/pull/790 .

2)  fexecve doesn't exist on OpenBSD so add conditional compilation for it
    in unistd and in related tests.

    The only "reference" that I could find is a mention that fexecve is
    not implemented on OpenBSD in the manual pages for signal(3) and
    sigaction(2):

    Official repository (search for "fexecve"):
    https://cvsweb.openbsd.org/src/lib/libc/sys/sigaction.2?rev=1.75&content-type=text/x-cvsweb-markup

    Github mirror:
    https://github.com/openbsd/src/blob/master/lib/libc/sys/sigaction.2#L619

3)  AIO doesn't work on OpenBSD so put test_aio_drop under conditional
    compilation.

4)  Add relevant changelog entries.

P.S. On OpenBSD remains the issue of test_scm_rights which builds
correctly but fails at runtime.

3 files changed, 33 insertions, 11 deletions

diff --git a/test/sys/test_aio_drop.rs b/test/sys/test_aio_drop.rs
index 1f4a3e79..492da401 100644
--- a/test/sys/test_aio_drop.rs
+++ b/test/sys/test_aio_drop.rs
@@ -1,18 +1,23 @@
 extern crate nix;
 extern crate tempfile;
 
-use nix::sys::aio::*;
-use nix::sys::signal::*;
-use std::os::unix::io::AsRawFd;
-use tempfile::tempfile;
-
 // Test dropping an AioCb that hasn't yet finished.
 // This must happen in its own process, because on OSX this test seems to hose
 // the AIO subsystem and causes subsequent tests to fail
 #[test]
 #[should_panic(expected = "Dropped an in-progress AioCb")]
-#[cfg(not(target_env = "musl"))]
+#[cfg(all(not(target_env = "musl"),
+          any(target_os = "linux",
+              target_os = "ios",
+              target_os = "macos",
+              target_os = "freebsd",
+              target_os = "netbsd")))]
 fn test_drop() {
+    use nix::sys::aio::*;
+    use nix::sys::signal::*;
+    use std::os::unix::io::AsRawFd;
+    use tempfile::tempfile;
+
     const WBUF: &[u8] = b"CDEF";
 
     let f = tempfile().unwrap();
diff --git a/test/test_stat.rs b/test/test_stat.rs
index 9d27ce79..fae8df82 100644
--- a/test/test_stat.rs
+++ b/test/test_stat.rs
@@ -7,7 +7,14 @@ use std::time::{Duration, UNIX_EPOCH};
 use libc::{S_IFMT, S_IFLNK};
 
 use nix::fcntl;
-use nix::sys::stat::{self, fchmod, fchmodat, futimens, lutimes, stat, utimes, utimensat};
+use nix::sys::stat::{self, fchmod, fchmodat, futimens, stat, utimes, utimensat};
+#[cfg(any(target_os = "linux",
+          target_os = "haiku",
+          target_os = "ios",
+          target_os = "macos",
+          target_os = "freebsd",
+          target_os = "netbsd"))]
+use nix::sys::stat::lutimes;
 use nix::sys::stat::{Mode, FchmodatFlags, UtimensatFlags};
 
 #[cfg(not(any(target_os = "netbsd")))]
@@ -196,6 +203,12 @@ fn test_utimes() {
 }
 
 #[test]
+#[cfg(any(target_os = "linux",
+          target_os = "haiku",
+          target_os = "ios",
+          target_os = "macos",
+          target_os = "freebsd",
+          target_os = "netbsd"))]
 fn test_lutimes() {
     let tempdir = tempfile::tempdir().unwrap();
     let target = tempdir.path().join("target");
diff --git a/test/test_unistd.rs b/test/test_unistd.rs
index ead4b487..3fb50535 100644
--- a/test/test_unistd.rs
+++ b/test/test_unistd.rs
@@ -230,16 +230,20 @@ cfg_if!{
         execve_test_factory!(test_execve, execve, &CString::new("/system/bin/sh").unwrap());
         execve_test_factory!(test_fexecve, fexecve, File::open("/system/bin/sh").unwrap().into_raw_fd());
     } else if #[cfg(any(target_os = "freebsd",
-                        target_os = "linux",
-                        target_os = "openbsd"))] {
+                        target_os = "linux"))] {
         execve_test_factory!(test_execve, execve, &CString::new("/bin/sh").unwrap());
         execve_test_factory!(test_fexecve, fexecve, File::open("/bin/sh").unwrap().into_raw_fd());
     } else if #[cfg(any(target_os = "dragonfly",
                         target_os = "ios",
                         target_os = "macos",
-                        target_os = "netbsd"))] {
+                        target_os = "netbsd",
+                        target_os = "openbsd"))] {
         execve_test_factory!(test_execve, execve, &CString::new("/bin/sh").unwrap());
-        // No fexecve() on DragonFly, ios, macos, and NetBSD.
+        // No fexecve() on DragonFly, ios, macos, NetBSD, OpenBSD.
+        //
+        // Note for NetBSD and OpenBSD: although rust-lang/libc includes it
+        // (under unix/bsd/netbsdlike/) fexecve is not currently implemented on
+        // NetBSD nor on OpenBSD.
     }
 }