[clang] nolock/noalloc attributes (PR #84983)

[Doug Wyatt via cfe-commits]

================
@@ -1402,6 +1402,29 @@ def CXX11NoReturn : InheritableAttr {
   let Documentation = [CXX11NoReturnDocs];
 }
 
+def NoLock : DeclOrTypeAttr {
+  let Spellings = [CXX11<"clang", "nolock">,
+                   C23<"clang", "nolock">,
+                   GNU<"clang_nolock">];
+
+  // Subjects - not needed?
+  //let Subjects = SubjectList<[FunctionLike, Block, TypedefName], ErrorDiag>;
----------------
dougsonos wrote:

I was cribbing from AnnotateType which also has no Subjects. I added these tests, which seem to indicate that type attributes have some built-in defense.
```
int nl_var [[clang::nolock]]; // expected-warning {{ 'nolock' only applies to function types; type here is 'int' }}
struct nl_struct {} [[clang::nolock]]; // expected-warning {{ attribute 'nolock' is ignored, place it after "struct" to apply attribute to type declaration }}
struct [[clang::nolock]] nl_struct2 {}; // expected-error {{ 'nolock' attribute cannot be applied to a declaration }}
```

https://github.com/llvm/llvm-project/pull/84983