llvm.global_[cd]tor is defined to be either external, or appending with an array

llvm.global_[cd]tor is defined to be either external, or appending with an array
of { i32, void ()* }. Teach the verifier to verify that, deleting copies of
checks strewn about.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129128 91177308-0d34-0410-b5e6-96231b3b80d8