Don't call doFinalization from verifyFunction.

verifyFunction needs to call doInitialization to collect metadata and avoid
crashing when verifying debug info in a function.

But it should not call doFinalization since that is where the verifier will
check declarations, variables and aliases, which is not desirable when one
only wants to verify a function.

A possible cleanup would be to split the class into a ModuleVerifier and
FunctionVerifier.

Issue reported by Ilia Filippov. Patch by Michael Kruse.

llvm-svn: 194574