Add build option to force building without external libudfread

I am trying to add a build option to force building without the external libudfread if it happens to exist. I ran into an issue with HandBrake where it builds with embedded copies of libbluray / libdvd* bits, but libbluray picks up the external copy of libudfread and then the build fails later on.

I started on this and think this is mostly how it should be but I'm struggling to find the syntax error with what I have.