Update libcdr.rb

Added 
+ @mnin https://github.com/mnin/homebrew/commit/c9cbb6cbc00a82079a70d438667f0048fd70f48b
+ @mikemcquaid https://github.com/Homebrew/homebrew/pull/31162/#discussion_r15633816
still waiting on @dtardon to help me understand how to tell libcdr where to install via a make flag https://github.com/Homebrew/homebrew/pull/31162/#discussion_r15633822