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.

1 files changed, 8 insertions, 4 deletions

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.
     }
 }