Begin work consolidating ShouldDelete* functions.

Begin with just default constructors. One note is that as a side effect
of this, a conformance test was removed on the basis that this is almost
certainly a defect as with most of union initialization. As it is, clang
does not implement union initialization close to the standard as it's
quite broken as written. I hope to write a paper addressing the issues
eventually.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@141528 91177308-0d34-0410-b5e6-96231b3b80d8