[LVI] Extend select handling to catch min/max/clamp idioms

[LVI] Extend select handling to catch min/max/clamp idioms

Most of this is fairly straight forward. Add handling for min/max via existing matcher utility and ConstantRange routines.  Add handling for clamp by exploiting condition constraints on inputs.

Note that I'm only handling two constant ranges at this point. It would be reasonable to consider treating overdefined as a full range if the instruction is typed as an integer, but that should be a separate change.

Differential Revision: http://reviews.llvm.org/D17184

llvm-svn: 262085