Revert "Don't use comdats for initializers on platforms that don't support it"

On further investigation, COMDATs should work with .ctors, and the issue
I was hitting probably reproduces with .init_array.

This reverts commit r218287.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218313 91177308-0d34-0410-b5e6-96231b3b80d8