my_sync() fails to use NtFlushBuffersFileEx()

MDEV-24037 implemented an optimization of the InnoDB specific os_file_flush_func() so that the system library function NtFlushBuffersFileEx() will be invoked when available, instead of the more costly FlushFileBuffers(). These functions are analogous to the POSIX functions fdatasync(2) and fsync(2).

The function my_sync(), which is being used outside InnoDB, is still solely relying on FlushFileBuffers(). To my understanding, this function is being invoked during DDL operations or when a non-default value of sync_binlog=1 (MDEV-16589) is being used.