More constructor cleanup.

Move to a single constructor with a default argument and avoid
the check and nullification.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187014 91177308-0d34-0410-b5e6-96231b3b80d8
Remove unnecessary constructors as the default conversions will handle
all enumerated cases. Reformat the rest of the existing constructors to
match.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187015 91177308-0d34-0410-b5e6-96231b3b80d8
Update testing cases to make them pass debug info verification.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187016 91177308-0d34-0410-b5e6-96231b3b80d8
Remove dead code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187017 91177308-0d34-0410-b5e6-96231b3b80d8
Replace with a "null" RAUW with an assert since we'd actually like
to assume we're replacing. Clarify comments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187018 91177308-0d34-0410-b5e6-96231b3b80d8