DwarfDebug: Allocate DIEValues with a BumpPtrAllocator. Most of them are

DwarfDebug: Allocate DIEValues with a BumpPtrAllocator. Most of them are
POD-like anyway, so we don't even care about calling their d'tors (DIEBlock
being the exception).

~6% less mallocs and ~1% compile time improvement on clang -O0 -g oggenc.c

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100035 91177308-0d34-0410-b5e6-96231b3b80d8