WASI: Implement fd_datasync

[kkebo]

I added implementation of fd_datasync following fd_sync #180.

• On Darwin
  • behaves exactly like fd_sync (fcntl(fd, F_FULLFSYNC))
• On Windows
  • behaves exactly like fd_sync (FlushFileBuffers)
• On UNIX-like systems except for Darwin
  • uses fdatasync(fd)
• On other systems that don't have fdatasync (e.g. Haiku)
  • uses fsync(fd) instead

References:

• https://github.com/WebAssembly/WASI/blob/9df56e7b858ca9a1a47d2cf8bbcf5391e3f5d773/legacy/preview1/docs.md#-fd_datasyncfd-fd---result-errno
• https://wasix.org/docs/api-reference/wasi/fd_datasync
• Darwin
  • https://transactional.blog/blog/2022-darwins-deceptive-durability
  • https://github.com/rust-lang/rust/blob/f1bc669636023c8643602431791c7f26e5a6edef/library/std/src/sys/fs/unix.rs#L1224
• Windows
  • https://github.com/rust-lang/rust/blob/f1bc669636023c8643602431791c7f26e5a6edef/library/std/src/sys/fs/windows.rs#L348

[kkebo]

This PR currently contains #180's commits.

[kateinoigakukun]

Thanks!