Move summary dead stripping before regular LTO.

This way dead stripping results are recorded in combined summary and
can be used in regular LTO passes.

Differential Revision: https://reviews.llvm.org/D33615

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304577 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed