Use 12 as the magic number for our abbreviation data and our
die values. A lot of DIEs have 10 attributes in C++ code (example
clang), none had more than 12. Seems like a good default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178366 91177308-0d34-0410-b5e6-96231b3b80d8