Adding additional argument for custom build options

Now it is possible to set additional compiler specific build options to
CMake via ant. This is e.g. needed if you would like to do parallel builds
by setting -j5.

Change-Id: Ibaa89841512a9ad087fed37618988f11d2a87565

git-svn-id: https://svn.apache.org/repos/asf/etch/trunk@1578855 13f79535-47bb-0310-9956-ffa450edef68