libbluray: fix compilation

The formula was assuming a head build (calling ./bootstrap) and depending on
automake/libtool. Add the proper conditionals to make it work with both stable
releases and in the HEAD variant. Also add :autoconf dependency. It doesn't
make any difference since te formula already adds a dependency on autotools
with :automake but since this project uses both this seems better from a
semantics perspective.

Also add libxml2 CFLAGS and remove the `--disable-debug` since it's going away
in future releases.