On PHP 7.1 and later, filesystem functions on Windows
use the Unicode system functions, which makes our file
handling work for non-ASCII file names.
Previously this was blacklisted for Windows on all PHP
versions. Versions before 7.1 will still reject Unicode
filenames with non-ASCII chars.
Bug: T3780
Change-Id: I94377faa5185f133be2dfb7b9b6aeacbd582834f