add a cl::opt override for TargetLoweringBase's JumpIsExpensive

add a cl::opt override for TargetLoweringBase's JumpIsExpensive

This patch is not intended to change existing codegen behavior for any target.
It just exposes the JumpIsExpensive setting on the command-line to allow for
easier testing and emergency overrides.

Also, change the existing regression test to use FileCheck, explicitly specify
the jump-is-expensive option, and use more precise checks.

Differential Revision: http://reviews.llvm.org/D10846

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241179 91177308-0d34-0410-b5e6-96231b3b80d8