On W32 libdvdread unconditionally uses msvc/contrib/dlfcn.c
While this allows libdvdread to be compiled out of the box, it
prevents it from linking to any other dlfcn implementation. Namely -
to dlfcn-win32 [1] (which is somewhat more POSIX-compliant).

Note that LDFLAGS modification should go AFTER (!) all AC_CHECK_LIB
calls, because -no-undefined is no longer valid as a compiler option.

[1] http://code.google.com/p/dlfcn-win32/