[Localizer] Don't trick to be smart for the insertion point

[Localizer] Don't trick to be smart for the insertion point

There is no guarantee that the first use of a constant that is traversed
is actually the first in the related basic block. Thus, if we use that
as the insertion point we may end up with definitions that don't
dominate there use.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304244 91177308-0d34-0410-b5e6-96231b3b80d8