[NewPassManager] Run global dead code elimination after the inliner.

[NewPassManager] Run global dead code elimination after the inliner.

This is the same exact change we did for the current pass manager
in rL314997, but the new pass manager pipeline already happened
to run GlobalOpt after the inliner, so we just insert a run of
GDCE here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315003 91177308-0d34-0410-b5e6-96231b3b80d8