[PATCH] [Runtime Unrolling] use a loop to simplify the runtime unrolling prologue.

[hfinkel at anl.gov]

Do we need to add unrolling metadata to the prologue so that we don't re-unroll the prologue if we run the unrolling pass twice? Even though this does not happen in the current pipeline setup, it could potentially happen with a different setup (or with LTO, etc.).

http://reviews.llvm.org/D5147