speeding up builds with ext4 and ccache tuning

[Dan Kegel]

Two more things:
- ccache's cache size matters.  If ccache -s shows the cache is full
  after two builds, try raising it.  The default is 1 GB, and I think
  with gcc-2.95, I needed a slightly larger cache.

- ccache might slow you down if you have less than 3GB of RAM.