Everywhere: Make Lagom build with GCC 13

GCC 13 was released on 2023-04-26. This commit fixes Lagom build errors
when using an updated host toolchain:
- Adds a workaround for a bug in constraint handling, which made LibJS
  fail to compile: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109683
- Silences the new `-Wdangling-reference` diagnostic globally. It
  produces multiple false positives with no clear way to silence them
  without `#pragmas`.
- Silences `-Wself-move` in `RefPtr` tests as GCC 13 adds this
  previously Clang-exclusive warning.

Tests/AK/TestRefPtr.cpp

@@ -97,14 +97,11 @@ TEST_CASE(assign_moved_self)
 {
     RefPtr<Object> object = adopt_ref(*new Object);
     EXPECT_EQ(object->ref_count(), 1u);
-#if defined(AK_COMPILER_CLANG)
-#    pragma clang diagnostic push
-#    pragma clang diagnostic ignored "-Wself-move"
-#endif
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpragmas"
+#pragma GCC diagnostic ignored "-Wself-move"
     object = move(object);
-#if defined(AK_COMPILER_CLANG)
-#    pragma clang diagnostic pop
-#endif
+#pragma GCC diagnostic pop
     EXPECT_EQ(object->ref_count(), 1u);
 }