dio_truncate truncates a file to at most offset bytes in size.
If the file previously was larger than this size, the extra data is lost. If the file previously was shorter, it is unspecified whether the file is left unchanged or is extended. In the latter case the extended part reads as zero bytes.
The file descriptor returned by dio_open.
The offset in bytes.
Returns true on success or false on failure.
This function is not implemented on Windows platforms.