[DSE] Enable removal of lifetime intrinsics in terminating blocks

Usually DSE is not supposed to remove lifetime intrinsics, but it's
actually ok to remove them for dead objects in terminating blocks,
because they convey no extra information there. Until we hit a lifetime
start that cannot be removed, that is. Because from that point on the
lifetime intrinsics become interesting again, e.g. for stack coloring.

Reviewers: reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11710

llvm-svn: 245542