[PATCH] [AArch64] Enable partial unrolling and runtime unrolling for AArch64 target

[Renato Golin]

By the comments, looks like this is just the value that ended up not bloating too much but still giving some performance. I think this is a lot more acceptable than before, though I'm not sure about when this will run. If this ends up only affecting -O2/3 (maybe even O1), it should be fine. But O0, Os and Oz need to skip anything depending on this.

Do we care that the relationship between the two (opt level and buffer size) are undocumented and de-coupled?

http://reviews.llvm.org/D5148