message: Change linkage type of modules to external after dropping initializers
  It isn't legal to have private global variables without initializers.  In the
  current state the -noconst.ll LLVM IR cannot be passed to opt.
diff: @@ -20,6 +20,7 @@ limitations under the License.
  #include <vector>
  #include "llvm/IR/DerivedTypes.h"
  +#include "llvm/IR/GlobalValue.h"
  #include "llvm/IR/MDBuilder.h"
  #include "llvm/IR/Operator.h"
  #include "llvm/Target/TargetOptions.h"
  @@ -67,6 +68,7 @@ std::unique_ptr<llvm::Module> DropConstantInitializers(
  std::unique_ptr<llvm::Module> cloned_module = CloneModule(&module);
  for (llvm::GlobalVariable& global_var : cloned_module->globals()) {
  global_var.setInitializer(nullptr);
  + global_var.setLinkage(llvm::GlobalValue::LinkageTypes::ExternalLinkage);
  }
  return cloned_module;
  }
  