Increase the dependence-analysis compute out

Increase the dependence-analysis compute out

As Polly got a lot faster after the small-integer-optimization imath
patch, we now increase the compute out to optimize larger kernels. This
should also expose additional slow-downs for us to address.

In LNT this gives us a 3.4x speedup on 3mm, at a cost of a 2x increase in
compile time (now 0.77s). reg_detect, oorafft and adi also show some compile
time increases. This compile time cost is divided between more time in isl and
more time in LLVM's backends due to increased code size (versioning and tiling).

llvm-svn: 240840