[clang] [Clang] Access tls_guard via llvm.threadlocal.address (PR #96633)

[Chuanqi Xu via cfe-commits]

================
@@ -1059,9 +1059,15 @@ CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
     if (Guard.isValid()) {
       // If we have a guard variable, check whether we've already performed
       // these initializations. This happens for TLS initialization functions.
-      llvm::Value *GuardVal = Builder.CreateLoad(Guard);
-      llvm::Value *Uninit = Builder.CreateIsNull(GuardVal,
-                                                 "guard.uninitialized");
+      Address GuardAddr = Guard;
+      if (auto *GV = dyn_cast<llvm::GlobalValue>(Guard.getPointer()))
+        // Get the thread-local address via intrinsic.
+        if (GV->isThreadLocal())
----------------
ChuanqiXu9 wrote:

```suggestion
      // Get the thread-local address via intrinsic.
      if (auto *GV = dyn_cast<llvm::GlobalValue>(Guard.getPointer());
           GV && GV->isThreadLocal())
```

https://github.com/llvm/llvm-project/pull/96633