[CodeView] Add support for content hashing CodeView type records.

Currently nothing uses this, but this at least gets the core
algorithm in, and adds some test to demonstrate correctness.

Differential Revision: https://reviews.llvm.org/D40736

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319854 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed