[llvm] [Support] Handle delete_pending case for Windows fs::status (PR #90655)

[Alexandre Ganea via llvm-commits]

================
@@ -786,8 +796,28 @@ std::error_code status(const Twine &path, file_status &result, bool Follow) {
   DWORD Flags = FILE_FLAG_BACKUP_SEMANTICS;
   if (!Follow) {
     DWORD attr = ::GetFileAttributesW(path_utf16.begin());
----------------
aganea wrote:

WDYT about moving the "delete pending" check into `llvm::mapWindowsError()`
```
std::error_code llvm::mapWindowsError(unsigned EV) {
  // Special case
  if (EV == ERROR_ACCESS_DENIED) {
    llvm::errc code = RtlGetLastNtStatus() == STATUS_DELETE_PENDING
                          ? errc::delete_pending
                          : errc::permission_denied;
    return make_error_code(code);
  }
  switch (EV) {
    MAP_ERR_TO_COND(ERROR_ALREADY_EXISTS, file_exists);
    MAP_ERR_TO_COND(ERROR_BAD_NETPATH, no_such_file_or_directory);
...
```
and then shorten this loop a bit?
```
    for (int Retry = 200; Retry >= 0; --Retry) {
      attr = ::GetFileAttributesW(path_utf16.begin());
      if (attr != INVALID_FILE_ATTRIBUTES)
        break;
      llvm::errc code = getStatus(INVALID_HANDLE_VALUE, result);
      if (code != llvm::errc::delete_pending || !Retry)
		return code;
      ::Sleep(10);
    }
```
Also, add maybe a comment above to the effect of "we're calling this internal NT API here after `GetLastError()` because it retrieves a more precise error code after internal kernel calls".

https://github.com/llvm/llvm-project/pull/90655