Replace macros with C++17 features (see issue #3362)

- Convert ALLOW_UNUSED_LOCAL to [[maybe_unused]]
- Convert WARN_UNUSED_RESULT to [[nodiscard]]

include/base/cef_scoped_refptr.h

@@ -46,7 +46,6 @@
 #include <type_traits>
 #include <utility>
 
-#include "include/base/cef_compiler_specific.h"
 #include "include/base/cef_logging.h"
 
 template <class T>
@@ -289,7 +288,7 @@ class TRIVIAL_ABI scoped_refptr {
 
   // Returns the owned pointer (if any), releasing ownership to the caller. The
   // caller is responsible for managing the lifetime of the reference.
-  T* release() WARN_UNUSED_RESULT;
+  [[nodiscard]] T* release();
 
   void swap(scoped_refptr& r) noexcept { std::swap(ptr_, r.ptr_); }