Verifier: Simplify and fix issue where we were not verifying unmaterialized functions.

Arrange to call verify(Function &) on each function, followed by
verify(Module &), whether the verifier is being used from the pass or
from verifyModule(). As a side effect, this fixes an issue that caused
us not to call verify(Function &) on unmaterialized functions from
verifyModule().

Differential Revision: http://reviews.llvm.org/D21042

llvm-svn: 271956