[wasi-common]: move filetime module to yanix (#1255)

* Move filetime module to yanix

I've noticed that we could replace every occurrence of `crate::Result`
in `filetime` mods with `io::Result`, so I thought why not move it
to `yanix` and get rid off a lot of unnecessary code duplication
within `wasi-common`. Now, ideally I'd have our `filetime` modifications
backported to Alex's [`filetime`] crate, but one step at a time
(apologies Alex, I was meant to backport this ages ago, just didn't
find the time yet... :-().

Anyway, this commit does just that; i.e., moves the `filetime` modules
into `yanix` which seems a better fit for this type of code.

[`filetime`]: https://github.com/alexcrichton/filetime

There is one caveat here. On Emscripten, converting between `filetime::Filetime`
and `libc::timespec` appears to be lossy, at least as far as the
types are concerned. Now, `filetime::Filetime`'s seconds field is
`i64` while nanoseconds field is `u32`, while Emscripten's
`libc::timespec` requires both to be `i32` width. This might actually
not be a problem since I don't think it's possible to fill `filetime::Filetime`
struct with values of width wider than `i32` since Emscripten is 32bit
but just to be on the safe side, we do a `TryInto` conversion, log
the error (if any), and return `libc::EOVERFLOW`.

* Run cargo fmt

* Use i64::from instead of as cast

crates/wasi-common/src/sys/unix/emscripten/filetime.rs

@@ -1,36 +0,0 @@
-//! This internal module consists of helper types and functions for dealing
-//! with setting the file times specific to Emscripten.
-use crate::{sys::unix::filetime::FileTime, Result};
-use std::fs::File;
-use std::io;
-
-pub(crate) const UTIME_NOW: i32 = 1_073_741_823;
-pub(crate) const UTIME_OMIT: i32 = 1_073_741_822;
-
-/// Wrapper for `utimensat` syscall. In Emscripten, there is no point in dynamically resolving
-/// if `utimensat` is available as it always was and will be.
-pub(crate) fn utimensat(
-    dirfd: &File,
-    path: &str,
-    atime: FileTime,
-    mtime: FileTime,
-    symlink_nofollow: bool,
-) -> Result<()> {
-    use crate::sys::unix::filetime::to_timespec;
-    use std::ffi::CString;
-    use std::os::unix::prelude::*;
-
-    let flags = if symlink_nofollow {
-        libc::AT_SYMLINK_NOFOLLOW
-    } else {
-        0
-    };
-    let p = CString::new(path.as_bytes())?;
-    let times = [to_timespec(&atime)?, to_timespec(&mtime)?];
-    let rc = unsafe { libc::utimensat(dirfd.as_raw_fd(), p.as_ptr(), times.as_ptr(), flags) };
-    if rc == 0 {
-        Ok(())
-    } else {
-        Err(io::Error::last_os_error().into())
-    }
-}

crates/wasi-common/src/sys/unix/emscripten/mod.rs

@@ -1,4 +1,3 @@
-pub(crate) mod filetime;
 #[path = "../linux/host_impl.rs"]
 pub(crate) mod host_impl;
 #[path = "../linux/hostcalls_impl.rs"]