wasi-common error cleanup: part 1, yanix (#1226)

* Reuse std::io::Error for raw *nix errno

This commit removes custom `yanix::Errno` and instead (as was
previously suggested) reuses `std::io::Error` to generate and wrap
raw *nix errno value.

* Update wasi-common to use new Yanix error type

This commit updates `wasi-common` to use new way of handling raw
OS error in `yanix`; i.e., via re-use of `std::io::Error` instead
of a custom `Errno` enum.

* Fix formatting

* Unwrap if io::Error created from raw OS error

This commit calls `unwrap` on `err` if that one was created via
`io::Error::last_os_error()`. It also refactors error matching
in several syscalls on the BSD platform (mainly).

crates/wasi-common/yanix/src/fcntl.rs

@@ -1,6 +1,6 @@
 use crate::{
     file::{FdFlag, OFlag},
-    Errno, Result,
+    Error, Result,
 };
 use std::os::unix::prelude::*;
 
@@ -9,7 +9,7 @@ pub unsafe fn dup_fd(fd: RawFd, close_on_exec: bool) -> Result<RawFd> {
     // the minimum duplicated RawFd number. In our case, I don't
     // think we have to worry about this that much, so passing in
     // the RawFd descriptor we want duplicated
-    Errno::from_result(if close_on_exec {
+    Error::from_result(if close_on_exec {
         libc::fcntl(fd, libc::F_DUPFD_CLOEXEC, fd)
     } else {
         libc::fcntl(fd, libc::F_DUPFD, fd)
@@ -17,17 +17,17 @@ pub unsafe fn dup_fd(fd: RawFd, close_on_exec: bool) -> Result<RawFd> {
 }
 
 pub unsafe fn get_fd_flags(fd: RawFd) -> Result<FdFlag> {
-    Errno::from_result(libc::fcntl(fd, libc::F_GETFD)).map(FdFlag::from_bits_truncate)
+    Error::from_result(libc::fcntl(fd, libc::F_GETFD)).map(FdFlag::from_bits_truncate)
 }
 
 pub unsafe fn set_fd_flags(fd: RawFd, flags: FdFlag) -> Result<()> {
-    Errno::from_success_code(libc::fcntl(fd, libc::F_SETFD, flags.bits()))
+    Error::from_success_code(libc::fcntl(fd, libc::F_SETFD, flags.bits()))
 }
 
 pub unsafe fn get_status_flags(fd: RawFd) -> Result<OFlag> {
-    Errno::from_result(libc::fcntl(fd, libc::F_GETFL)).map(OFlag::from_bits_truncate)
+    Error::from_result(libc::fcntl(fd, libc::F_GETFL)).map(OFlag::from_bits_truncate)
 }
 
 pub unsafe fn set_status_flags(fd: RawFd, flags: OFlag) -> Result<()> {
-    Errno::from_success_code(libc::fcntl(fd, libc::F_SETFL, flags.bits()))
+    Error::from_success_code(libc::fcntl(fd, libc::F_SETFL, flags.bits()))
 }