Patch for: 7132779: build-infra merge: Enable ccache to work for most developer builds.

[Fredrik Öhrström]

Hello hotspot-runtime-dev and build-dev!

This is a patch to enable ccache to work for all builds,
not only builds where the build number has been explicitly set.

Webrev is here:

http://cr.openjdk.java.net/~ohrstrom/7132779/webrev.00/

Exported hg patch is here:

http://cr.openjdk.java.net/~ohrstrom/7132779/webrev.00/7132779.patch

Is it good enough, so that you can commit for me Robert?

Thanks!
//Fredrik