Switch all builds from Travis to Cirrus

Travis has been super-slow lately (> 6 hours per build).  Cirrus is much
faster: about 20 minutes.  Cirrus also has slightly better test
coverage, mainly because it doesn't use SECCOMP.

Also,

* Fix the Redox CI build.  The old Travis configuration didn't actually
  build for Redox, so we never noticed that Redox can't be built with a
  stable compiler.  Thanks to @coolreader18 for finding this.

* Disable the udp_offload tests on cross-tested platforms.  These tests
  are failing with ENOPROTOOPT in Cirrus-CI.  I suspect it's due to a
  lack of support in QEMU.  These tests were skipped on Travis because
  its kernel was too old.

* Fix require_kernel_version on Cirrus-CI.  Cirrus reports the Linux
  kernel version as 4.19.112+, which the semver crate can't handle.

* Fix test_setfsuid on Cirrus.  When run on Cirrus, it seems like the
  file in /tmp gets deleted as soon as it's closed.  Probably an
  overzealous temporary file cleaner.  Use /var/tmp, because no
  temporary file cleaner should run in there.

* Skip mount tests on Cirrus.  They fail for an unknown reason.
Issue #1351

* Skip the AF_ALG tests on Cirrus-CI
Issue #1352

1 files changed, 2 insertions, 2 deletions

diff --git a/src/unistd.rs b/src/unistd.rs
index 04031e37..a945ac26 100644
--- a/src/unistd.rs
+++ b/src/unistd.rs
@@ -12,9 +12,9 @@ use libc::{self, c_char, c_void, c_int, c_long, c_uint, size_t, pid_t, off_t,
            uid_t, gid_t, mode_t, PATH_MAX};
 use std::{fmt, mem, ptr};
 use std::convert::Infallible;
-use std::ffi::{CStr, CString, OsString};
+use std::ffi::{CStr, OsString};
 #[cfg(not(target_os = "redox"))]
-use std::ffi::{OsStr};
+use std::ffi::{CString, OsStr};
 use std::os::unix::ffi::OsStringExt;
 #[cfg(not(target_os = "redox"))]
 use std::os::unix::ffi::OsStrExt;