fix(flock): check if they are marked unsupported in libstd (#15941)

### What does this PR try to resolve?

This is a follow-up of <#15935>.

Before this Cargo invokes syscalls and check whether it gets ENOTSUP to
determine flock is unsupported. However, now the "unsupported platforms"
are pre-defined by libstd. Cargo should perhaps return unsupported if a
platform is marked unsupported by libstd.

Without this, some people on Termux may be affected I guess?

See
https://github.com/rust-lang/rust/blob/e9b6085088fd671ecfbe4cbebe1d26796d8bfa30/library/std/src/sys/fs/unix.rs#L1395-L1410

Author: epage

src/cargo/util/flock.rs

@@ -435,13 +435,15 @@ fn error_unsupported(err: &std::io::Error) -> bool {
         #[allow(unreachable_patterns)]
         Some(libc::ENOTSUP | libc::EOPNOTSUPP) => true,
         Some(libc::ENOSYS) => true,
-        _ => false,
+        _ => err.kind() == std::io::ErrorKind::Unsupported,
     }
 }
 
 #[cfg(windows)]
 fn error_unsupported(err: &std::io::Error) -> bool {
     use windows_sys::Win32::Foundation::ERROR_INVALID_FUNCTION;
-    err.raw_os_error()
-        .map_or(false, |x| x == ERROR_INVALID_FUNCTION as i32)
+    match err.raw_os_error() {
+        Some(code) if code == ERROR_INVALID_FUNCTION as i32 => true,
+        _ => err.kind() == std::io::ErrorKind::Unsupported,
+    }
 }