Add calls to doInitialization() and doFinalization() in verifyFunction()

The function verifyFunction() in lib/IR/Verifier.cpp misses some
calls. It creates a temporary FunctionPassManager that will run a
single Verifier pass. Unfortunately, FunctionPassManager is no
PassManager and does not call doInitialization() and doFinalization()
by itself. Verifier does important tasks in doInitialization() such as
collecting type information used to check DebugInfo metadata and
doFinalization() does some additional checks. Therefore these checks
were missed and debug info couldn't be verified at all, it just
crashed if the function had some.

verifyFunction() is currently not used in llvm unless -debug option is
enabled, and in unittests/IR/VerifierTest.cpp

VerifierTest had to be changed to create the function in a module from
which the type debug info can be collected.

Patch by Michael Kruse.