[clang] Support [[guarded_by(mutex)]] attribute inside C struct (PR #94216)

[Yeoul Na via cfe-commits]

================
@@ -28,7 +28,12 @@
 struct LOCKABLE Mutex {};
 
 struct Foo {
-  struct Mutex *mu_;
+    struct Mutex *mu_;
+    struct Bar {
+        struct Mutex *other_mu;
+    } bar;
+  int  a_value GUARDED_BY(mu_);
----------------
rapidsna wrote:

Nit: Please check indent

https://github.com/llvm/llvm-project/pull/94216