[Replicant] Introducing ccache to Replicant 6

[Joonas Kylmälä]

Hi,

Denis 'GNUtoo' Carikli:
> Is there an advantage in building ccache when most GNU/Linux
> distributions already have it? 
> 
> Is it for making the build more reproducible? 
> Is it to make it more easy and have less dependencies?

In my opinion we should just use the distro ccache and that is what I
have been doing with Replicant 6 (if I remember right, long time ago
since last replicant 6 build). And GNUtoo, you asked about any issues: I
don't remember coming across any.

Joonas