Although I have ccache installed and configured -- and used by (most of) the ports, openjdk8's configure advises me of the following:
Build performance summary:
* Cores to use: 4
* Memory limit: 15776 MB
* ccache status: not installed (consider installing)
Build performance tip: ccache gives a tremendous speedup for C++ recompilations.
You do not have ccache installed. Try installing it.
Whatever it is, it is probably worth fixing...