[safestack] Fix compiler crash in the presence of stack restores.

A use can be emitted before def in a function with stack restore
points but no static allocas.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248455 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed