[ccache] ccacje direct mode without fall back to running the preprocessor

[Andrew Stubbs]

On 08/09/14 11:37, vkr wrote:
> If the env variable TRS_CCACHE_NO_PREPROCESSOR_ON_DIRECT_LOOKUP_MISS is set
> then, I do not run preprocessing, but just fall back to running real-compiler.
>
> I see a lot of time saving, and I can't think of any side-effect.

It's not the right implementation for the master branch, but might be ok 
in the release branch?

That's up to Joel.

Seems like a worthwhile feature, in read-only mode.

Andrew