[ccache] Intel compiler

[tridge at samba.org]

> Or perhaps ccache should just cache stdout.  distcc sends it across
> the network alongside stderr. 
> 
> I'm not sure why writing to stdout forces a cache miss.

It's because is also very hard to accurately cache both stderr and
stdout because of the timing of lines between them. To really
accurately cache them ccache would need to record not only what came
out of stdout and stderr, but exactly what order the lines came in, so
when it is replayed the output looks the same.

I'd be happy to add a CCACHE_IGNORE_STDOUT option which would help for
the intel compiler. I'm not convinced it is really worth actually
cacheing stdout, as the output will probably look pretty strange if we
just put all the stdout at the start or end.

Cheers, Tridge