Implement --enable-debuginfo to permit us to force building with debuginfo

There are two commits here. The second implements --enable-debuginfo for distributions that build modules without debuginfo. The first is a refactor of --enable-debug based on an observation made during the development of the first that --enable-debug=true would paradoxically become --disable-debug. The order is reversed to make cherry picking easier should anyone want to backport only the change to --enable-debug's argument semantics.