Extend the IL for selecting TLS models (PR9788)

This allows the user/front-end to specify a model that is better
than what LLVM would choose by default. For example, a variable
might be declared as

  @x = thread_local(initialexec) global i32 42

if it will not be used in a shared library that is dlopen'ed.

If the specified model isn't supported by the target, or if LLVM can
make a better choice, a different model may be used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159077 91177308-0d34-0410-b5e6-96231b3b80d8

lib/VMCore/IRBuilder.cpp

@@ -28,7 +28,7 @@ Value *IRBuilderBase::CreateGlobalString(StringRef Str, const Twine &Name) {
   Module &M = *BB->getParent()->getParent();
   GlobalVariable *GV = new GlobalVariable(M, StrConstant->getType(),
                                           true, GlobalValue::PrivateLinkage,
-                                          StrConstant, "", 0, false);
+                                          StrConstant);
   GV->setName(Name);
   GV->setUnnamedAddr(true);
   return GV;