[Fontconfig] Application startup performance

[Nick Alcock]

On 15 Jan 2016, Akira TAGOH said:

>> This patch will probably need changing in small ways if we care about
>> any systems on which dentry.d_type does not exist (probably we do: this
>> is just a proof of concept):
>
> Thanks. modified a bit for platforms which doesn't have d_type in
> dirent and the invalid cache issue when a directory contains a symlink
> to dir. it looks good so far. I'll test more and push into git then.

Great! Sorry for only doing half the job, but I don't have any
non-d_type-capable systems here so it seemed safer to only hack up an
ugly hack I could actually test.

I'll whip up something else this weekend to try to avoid the entire
readdir() (which is still happening), assuming we have a timestamp in
the cache that we can compare the directory as a whole to and assuming
we don't expect people to directly modify font files but rather write
out new ones so the timestamp in the directory gets updated. readdir()
is not remotely as expensive as a stat(), even on rotating rust like
mine, but it's still more or less pointless in the clean-cache case and
worth avoiding.

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NULL && (void)