title: ccache basedir doesn't work as expected
body: <p>I'm trying to make ccache work with the same source code built from different sibling directories. I've successfully set <code>CCACHE_BASEDIR</code> to the parent dir of these two siblings. If I do a build in <code>bld1</code> and then switch to <code>bld2</code> and build that copy (again, these are the same sources), I get no cache hits. </p>
  
  <p>I'm now looking at the log output from setting <code>CCACHE_LOGFILE</code>. Unfortunately the log doesn't tell me what factors/data went into computing the hashes it looks up, I just see lots of "No such manifest file" message (for direct lookup, it seems). </p>
  
  <p>Are there any other options I can use to debug the issue with ccache to figure out why it doesn't recognize these two source trees as identical?</p>
  
  <p>Just to be clear, if I repeat the build in a given directory, I do indeed get lots of hits in the cache - so clearly ccache is working with an unchanging build path, it just doesn't seem to be working properly across directories.</p>