[clang] [Clang][Sema]:Fix musttail attribute on a function with not_tail_called attribute has no warning/error (PR #134465)

[Aaron Ballman via cfe-commits]

================
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s
+
+int __attribute__((not_tail_called)) foo1(int a) {
+    return a + 1;  
+}
+
+
+int foo2(int a) {
+    [[clang::musttail]] 
+    return foo1(a);  // expected-error {{cannot perform a tail call to function 'foo1' because its signature is incompatible with the calling function}}
----------------
AaronBallman wrote:

Good idea Erich! I don't think we need a new diagnostic though, we can reuse `note_conflicting_attribute`, so I think this will suffice:
```
Diag(CalleeDecl->getAttr<NotTailCalledAttr>()->getLoc(), diag::note_conflicting_attribute);
```

https://github.com/llvm/llvm-project/pull/134465