[ccache] PATCH: Look at include files' mtimes

[Wilson Snyder]

>> Allowing multiple versions to co-reside and not trash each
>> other's result would be useful. =A0Presently I need redefine
>> CCACHE_DIR for each version to avoid overlap, which is
>> annoying. [...]
>
> From the top of my head, the issues I'm aware of regarding different
>ccache versions accessing the same cache directory are:
>
>* <3.1 throws away statistics counters from future ccache versions,
>which is annoying but shouldn't be critical.
>* <3.1 and >=3.1 have different methods of locking and updating the
>stats files. If you're unlucky, the stats files (including the cache
>size limits) could be garbled.
>
>Do you know of more issues than the above?

I don't know of specific recent issues.