[Libreoffice] ccache support

[Terrence Enger]

On Fri, 2011-09-09 at 14:22 -0500, Norbert Thiebaud wrote:
> 
> Now granted, once we can reliably do incremental build, the question
> of the effectiveness of ccache will be much more acute.
> presumable incremental build only try to compile stuff that _need_ to
> be compiled and therefore should be a ccache miss... so with perfect
> incremental build the ccache hit should be 0%

Not quite, I think.  Consider a header file changed within
in #if-skipped region in a way which does not change the
number of skipped lines.  I expect this would trigger a
recompile and that ccache, other things being equal, would
find a hit on the cache.  Does this sound plausible.

Still, I would expect the hit rate to go really close to 0.

Terry.