GlobalISel: stop localizer putting constants before EH_LABELs

GlobalISel: stop localizer putting constants before EH_LABELs

If the localizer pass puts one of its constants before the label that tells the
unwinder "jump here to handle your exception" then control-flow will skip it,
leaving uninitialized registers at runtime. That's bad.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308687 91177308-0d34-0410-b5e6-96231b3b80d8