Merge wasi-common into wasmtime

This commit merges [CraneStation/wasi-common] repo as a subdir of
this repo while preserving **all** of git history. There is an
initiative to pull `wasi-common` into [CraneStation/wasmtime], and
[CraneStation/wasmtime] becoming a monorepo. This came about for
several reasons with a common theme of convenience, namely,
having a monorepo:
1. cleans up the problem of dependencies (as we have seen first
   hand with dependabot enabled, it can cause some grief)
2. completely removes the problem of syncing the closely dependent
   repos (e.g., updating `wasi-common` with say a bugfix generally
   implies creating a "sync" commit for pulling in the changes into
   the "parent" repo, in this case, `wasmtime`)
3. mainly for the two reasons above, makes publishing to crates.io
   easier
4. hopefully streamlines the process of getting the community
   involved in contributing to `wasi-common` as now everything
   is one place

[CraneStation/wasi-common]: https://github.com/CraneStation/wasi-common
[CraneStation/wasmtime]: https://github.com/CraneStation/wasmtime

wasi-common/src/sys/unix/bsd/mod.rs

@@ -0,0 +1,82 @@
+pub(crate) mod hostcalls_impl;
+pub(crate) mod osfile;
+
+pub(crate) mod fdentry_impl {
+    use crate::{sys::host_impl, Result};
+    use std::os::unix::prelude::AsRawFd;
+
+    pub(crate) unsafe fn isatty(fd: &impl AsRawFd) -> Result<bool> {
+        let res = libc::isatty(fd.as_raw_fd());
+        if res == 1 {
+            // isatty() returns 1 if fd is an open file descriptor referring to a terminal...
+            Ok(true)
+        } else {
+            // ... otherwise 0 is returned, and errno is set to indicate the error.
+            match nix::errno::Errno::last() {
+                nix::errno::Errno::ENOTTY => Ok(false),
+                x => Err(host_impl::errno_from_nix(x)),
+            }
+        }
+    }
+}
+
+pub(crate) mod host_impl {
+    use super::super::host_impl::dirent_filetype_from_host;
+    use crate::{wasi, Result};
+
+    pub(crate) const O_RSYNC: nix::fcntl::OFlag = nix::fcntl::OFlag::O_SYNC;
+
+    pub(crate) fn dirent_from_host(
+        host_entry: &nix::libc::dirent,
+    ) -> Result<wasi::__wasi_dirent_t> {
+        let mut entry = unsafe { std::mem::zeroed::<wasi::__wasi_dirent_t>() };
+        let d_type = dirent_filetype_from_host(host_entry)?;
+        entry.d_ino = host_entry.d_ino;
+        entry.d_next = host_entry.d_seekoff;
+        entry.d_namlen = u32::from(host_entry.d_namlen);
+        entry.d_type = d_type;
+        Ok(entry)
+    }
+}
+
+pub(crate) mod fs_helpers {
+    use cfg_if::cfg_if;
+
+    pub(crate) fn utime_now() -> libc::c_long {
+        cfg_if! {
+            if #[cfg(any(
+                    target_os = "macos",
+                    target_os = "freebsd",
+                    target_os = "ios",
+                    target_os = "dragonfly"
+            ))] {
+                -1
+            } else if #[cfg(target_os = "openbsd")] {
+                // https://github.com/openbsd/src/blob/master/sys/sys/stat.h#L187
+                -2
+            } else if #[cfg(target_os = "netbsd" )] {
+                // http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/sys/stat.h?rev=1.69&content-type=text/x-cvsweb-markup&only_with_tag=MAIN
+                1_073_741_823
+            }
+        }
+    }
+
+    pub(crate) fn utime_omit() -> libc::c_long {
+        cfg_if! {
+            if #[cfg(any(
+                    target_os = "macos",
+                    target_os = "freebsd",
+                    target_os = "ios",
+                    target_os = "dragonfly"
+            ))] {
+                -2
+            } else if #[cfg(target_os = "openbsd")] {
+                // https://github.com/openbsd/src/blob/master/sys/sys/stat.h#L187
+                -1
+            } else if #[cfg(target_os = "netbsd")] {
+                // http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/sys/stat.h?rev=1.69&content-type=text/x-cvsweb-markup&only_with_tag=MAIN
+                1_073_741_822
+            }
+        }
+    }
+}