[ccache] Why not cache compile failures?

[Justin Lebar]

> I'm looking at ways to improve compile speed, and one obvious option is to
> cache compile failures. I'm thinking of certain non-called-for-link autoconf
> tests, in particular.

Doesn't autoconf have a cache of its own?

Anyway, ccache makes running the compiler faster.  In the cause of
giving the compiler a small program to compile to test a feature,
surely running the compiler takes virtually zero time, and the
overhead is elsewhere.

-Justin