Add a separate llvm.global_ctors entry for linkonce_odr data initializers

Summary:
These typically come from static data members of class template
specializations.  This accomplishes two things:

1. May expose GlobalOpt optimizations for Itanium C++ ABI code.
2. Works toward fixing double initialization in the Microsoft C++ ABI.

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1475

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189051 91177308-0d34-0410-b5e6-96231b3b80d8