Fix several places that were calling verifyFunction or verifyModule without...

Fix several places that were calling verifyFunction or verifyModule without checking the return value.

verifyFunction/verifyModule don't assert or error internally. They
also don't print anything if you don't pass a raw_ostream to them.
So the caller needs to check the result and ideally pass a stream
to get the messages. Otherwise they're just really expensive no-ops.

I've filed PR45965 for another instance in SLPVectorizer
that causes a lit test failure.

Differential Revision: https://reviews.llvm.org/D80106