Revert "[Support] Replace HashString with djbHash."

Revert "[Support] Replace HashString with djbHash."

It looks like some of our tests depend on the ordering of hashed values.
I'm reverting my changes while I try to reproduce and fix this locally.

Failing builds:

  lab.llvm.org:8011/builders/lld-x86_64-darwin13/builds/18388
  lab.llvm.org:8011/builders/clang-cmake-x86_64-sde-avx512-linux/builds/6743
  lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast/builds/15607

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@326082 91177308-0d34-0410-b5e6-96231b3b80d8