[InstCombine] Fix div handling

When we optimize select basing on fact that div by 0 is undef
we should not traverse the instruction which are not guaranteed to
transfer execution to next instruction. Guard intrinsic is an example.

Reviewers: spatel, craig.topper
Reviewed By: spatel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D47576

llvm-svn: 333864