Bitcode: Change getModuleSummaryIndex() to return an llvm::Expected.

Differential Revision: https://reviews.llvm.org/D26539

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286624 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed