[NFC] [Coroutines] Add tests for looking up deallocation

According to [dcl.fct.def.coroutine]p12, the program should be
ill-formed if the promise_type contains operator delete but none of them
are available. But this behavior was not tested before. This commit adds
the tests for it.

clang/test/SemaCXX/coroutine-dealloc.cpp

@@ -0,0 +1,27 @@
+// Tests that the behavior will be good if there are multiple operator delete in the promise_type.
+// RUN: %clang_cc1 %s -std=c++20 %s -fsyntax-only -verify
+// expected-no-diagnostics
+
+#include "Inputs/std-coroutine.h"
+
+namespace std {
+    typedef __SIZE_TYPE__ size_t;
+    enum class align_val_t : size_t {};
+}
+
+struct task {
+  struct promise_type {
+    auto initial_suspend() { return std::suspend_always{}; }
+    auto final_suspend() noexcept { return std::suspend_always{}; }
+    auto get_return_object() { return task{}; }
+    void unhandled_exception() {}
+    void return_value(int) {}
+
+    void operator delete(void *ptr, void *meaningless_placeholder);
+    void operator delete(void *ptr);
+  };
+};
+
+task f() {
+  co_return 43;
+}

clang/test/SemaCXX/coroutine-no-valid-dealloc.cpp

@@ -0,0 +1,26 @@
+// Test that if the compiler will emit error message if the promise_type contain
+// operator delete but none of them are available. This is required by the standard.
+// RUN: %clang_cc1 %s -std=c++20 %s -fsyntax-only -verify
+
+#include "Inputs/std-coroutine.h"
+
+namespace std {
+    typedef __SIZE_TYPE__ size_t;
+    enum class align_val_t : size_t {};
+}
+
+struct task {
+  struct promise_type {
+    auto initial_suspend() { return std::suspend_always{}; }
+    auto final_suspend() noexcept { return std::suspend_always{}; }
+    auto get_return_object() { return task{}; }
+    void unhandled_exception() {}
+    void return_value(int) {}
+
+    void operator delete(void *ptr, void *meaningless_placeholder); // expected-note {{member 'operator delete' declared here}}
+  };
+};
+
+task f() { // expected-error 1+{{no suitable member 'operator delete' in 'promise_type'}}
+  co_return 43;
+}