Move the logic to avoid double global emission from Sema to CodeGen

Reverts the code changes from r234675 but keeps the test case.

We were already maintaining a DenseMap of globals with dynamic
initializers anyway.

Fixes the test case from PR23234.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@234961 91177308-0d34-0410-b5e6-96231b3b80d8

• lib/CodeGen/CGDeclCXX.cpp[diff]
• lib/CodeGen/CodeGenModule.h[diff]
• lib/Sema/SemaTemplateInstantiateDecl.cpp[diff]
• test/CodeGenCXX/auto-variable-template.cpp[Added - diff]