open with O_CLOEXEC

This fixes a problem with Tauri auto update: After updating the tauri
application it is restarted, but the serial files were not closed, and
therefore the application could not open them again.

With this flag the files are closed when executing `execve()` to start
the new application instance.

Change-Id: I102ba33411135a8e89e3203f9dad910d385feeee

src/posix/tty.rs

@@ -116,7 +116,7 @@ impl TTYPort {
         let path = Path::new(&builder.path);
         let fd = OwnedFd(nix::fcntl::open(
             path,
-            OFlag::O_RDWR | OFlag::O_NOCTTY | OFlag::O_NONBLOCK,
+            OFlag::O_RDWR | OFlag::O_NOCTTY | OFlag::O_NONBLOCK | OFlag::O_CLOEXEC,
             nix::sys::stat::Mode::empty(),
         )?);
 
@@ -344,7 +344,7 @@ impl TTYPort {
     ///
     /// This function returns an error if the serial port couldn't be cloned.
     pub fn try_clone_native(&self) -> Result<TTYPort> {
-        let fd_cloned: i32 = fcntl(self.fd, nix::fcntl::F_DUPFD(self.fd))?;
+        let fd_cloned: i32 = fcntl(self.fd, nix::fcntl::F_DUPFD_CLOEXEC(self.fd))?;
         Ok(TTYPort {
             fd: fd_cloned,
             exclusive: self.exclusive,