Adapt to llvm change r296992 to unbreak the bots

r296992 made ScalarEvolution's CompareValueComplexity less aggressive,
and that broke the polly test being fixed in this change.  This change
explicitly bumps CompareValueComplexity in said test case to make it
pass.

Can someone from the polly team please can give me an idea on if this
case is important enough to have
scalar-evolution-max-value-compare-depth be 3 by default?

llvm-svn: 296994