Vendor dependencies

Let's see how I like this workflow.

vendor/rustix/src/backend/libc/io/mod.rs

@@ -0,0 +1,13 @@
+pub(crate) mod errno;
+#[cfg(not(windows))]
+#[cfg(not(feature = "std"))]
+pub(crate) mod io_slice;
+pub(crate) mod poll_fd;
+#[cfg(not(windows))]
+pub(crate) mod types;
+
+#[cfg_attr(windows, path = "windows_syscalls.rs")]
+pub(crate) mod syscalls;
+
+#[cfg(any(target_os = "android", target_os = "linux"))]
+pub mod epoll;