Revert "AsmPrinter: Change DIEValue to be stored by value"

Revert "AsmPrinter: Change DIEValue to be stored by value"

This reverts commit r238349, since it caused some errors on bots:
  - std::is_trivially_copyable isn't available until GCC 5.0.
  - It was complaining about strict aliasing with my use of
    ArrayCharUnion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238350 91177308-0d34-0410-b5e6-96231b3b80d8