[Fontconfig] Fontconfig cache file update fails on Windows (also Cygwin)

[Masamichi Hosoda]

> Sorry, missed that. merged.
> 
> On Thu, Jun 1, 2017 at 1:11 AM, Werner LEMBERG <wl at gnu.org> wrote:
> 
>>
>> > On Windows (MinGW), fontconfig 2.12.3 still fails to update the font
>> > cache.
>>
>> Honestly spoken, it is hard to understand why this patch doesn't get
>> applied – even if the code might be considered as not optimal, it
>> solves a very serious issue *right now*.  It's always easy to revert
>> later on.

Thank you for merging it.