AK: Add a helper macro to temporarily ignore diagnostics with _Pragma()

AK/Diagnostics.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+// Needed to turn the 'name' token and the preceding 'GCC diagnostic ignored'
+// into a single string literal, it won't accept "foo"#bar concatenation.
+#define _AK_PRAGMA(x) _Pragma(#x)
+#define AK_PRAGMA(x) _AK_PRAGMA(x)
+
+// Helper macro to temporarily disable a diagnostic for the given statement.
+// Using _Pragma() makes it possible to use this in other macros as well (and
+// allows us to define it as a macro in the first place).
+// NOTE: 'GCC' is also recognized by clang.
+#define AK_IGNORE_DIAGNOSTIC(name, statement) \
+    AK_PRAGMA(GCC diagnostic push);           \
+    AK_PRAGMA(GCC diagnostic ignored name);   \
+    statement;                                \
+    AK_PRAGMA(GCC diagnostic pop);