DwarfDebug: Minor refactoring around type unit construction

Sinking addition of the declaration attribute down to where the
signature is added. So that if the signature is not added neither is the
declaration attribute (this will come in handy when aborting type unit
construction to instead emit the type into the CU directly in some
cases)

Pull out type unit identifier hashing just to simplify the function a
little, it'll be getting longer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207321 91177308-0d34-0410-b5e6-96231b3b80d8
Print X86ISD::PMULDQ nodes properly in debug output.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207322 91177308-0d34-0410-b5e6-96231b3b80d8