configure.ac: Remove cpp from topdirs.  configure lacks sufficient checks to ensure compilation, so easier to make it non-default.
configure.ac: Remove cpp from topdirs.  configure lacks sufficient checks to ensure compilation, so easier to make it non-default.

b1v1r/ironbee,ironbee/ironbee,ironbee/ironbee,b1v1r/ironbee,b1v1r/ironbee,ironbee/ironbee,b1v1r/ironbee,ironbee/ironbee,ironbee/ironbee,ironbee/ironbee,b1v1r/ironbee,ironbee/ironbee,ironbee/ironbee,b1v1r/ironbee,b1v1r/ironbee,b1v1r/ironbee,b1v1r/ironbee,b1v1r/ironbee,ironbee/ironbee,ironbee/ironbee,ironbee/ironbee,b1v1r/ironbee,ironbee/ironbee,b1v1r/ironbee