Clarify comments for types contained in anonymous namespaces and
odr hashes.
Make sure we don't emit an ODR hash for types with no name and make
sure the comments for each testcase are a bit easier to distinguish.
Fix a truly egregious thinko in anonymous namespace check,
update testcase to make sure we generate debug info for walrus
by adding a non-trivial constructor and verify that we don't
emit an ODR signature for the type.