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, 11 insertions, 6 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();