[ccache] Support for color diagnostics

[Lubos Lunak]

On Friday 29 of November 2013, Lubos Lunak wrote:
>  Hello,
>
>  the attached patch adds ccache support for compiler color diagnostics
> (also reported by somebody as #10075).
...
> Caveats:

 I forgot one:

- The function color_output_possible() may look simplistic, but as far as I 
can tell it works just fine (it's been in Incecream for a number of years).

-- 
 Lubos Lunak