Revert "Bitcode: Collect all MDString records into a single blob"

This reverts commit r264409 since it failed to bootstrap:
http://lab.llvm.org:8080/green/job/clang-stage2-configure-Rlto_build/8302/

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264410 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed