[PATCH] Prevent MDNode's RAUW from introducing a reference to a void Value.

[Frederic Riss]

Actually I should be able to easily extend the testcase to include a valid call to a bitcasted function type also (the fix changed scope, and the new one should be easier to test). I'd like to leave the UB call there for now as it is the initial issue that I chased, the one that caused an assert during bitcode serialization.

http://reviews.llvm.org/D5828