[InstCombine] allow narrowing of min/max/abs

We have bailout hacks based on min/max in various places in instcombine 
that shouldn't be necessary. The affected test was added for:
D48930 
...which is a consequence of the improvement in:
D48584 (https://reviews.llvm.org/rL336172)

I'm assuming the visitTrunc bailout in this patch was added specifically 
to avoid a change from SimplifyDemandedBits, so I'm just moving that 
below the EvaluateInDifferentType optimization. A narrow min/max is still
a min/max.

llvm-svn: 336293