ab: require apr, apr-util regardless of MacOS version

ab's configure spits the following error when --with-apr and/or --with-apr-util params are defined but fail to locate the corresponding dependencies.

"checking for APR... configure: error: the --with-apr parameter is incorrect. It must specify an install prefix, a build directory, or an apr-config file"

Both dependencies should be readily available before attempting to install ab regardless of the MacOS version.