This will help sneak undefs past GVN into the DAG for
some tests.
Also add missing intrinsic for rsq_legacy, even though the node
was already selected to the instruction. Also start passing
the debug location to intrinsic errors.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273181 91177308-0d34-0410-b5e6-96231b3b80d8
