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_compiler_specific.h

@@ -386,26 +386,4 @@ inline constexpr bool AnalyzerAssumeTrue(bool arg) {
 #endif
 
 #endif  // !USING_CHROMIUM_INCLUDES
-
-// Annotate a function indicating the caller must examine the return value.
-// Use like:
-//   int foo() WARN_UNUSED_RESULT;
-// To explicitly ignore a result, use std::ignore from <tuple>.
-// Alternately use `[[nodiscard]]` with code that supports C++17.
-#undef WARN_UNUSED_RESULT
-#if defined(COMPILER_GCC) || defined(__clang__)
-#define WARN_UNUSED_RESULT __attribute__((warn_unused_result))
-#else
-#define WARN_UNUSED_RESULT
-#endif
-
-// Annotate a variable indicating it's ok if the variable is not used.
-// (Typically used to silence a compiler warning when the assignment
-// is important for some other reason.)
-// Use like:
-//   int x = ...;
-//   ALLOW_UNUSED_LOCAL(x);
-// Alternately use `[[maybe_unused]]` with code that supports C++17.
-#define ALLOW_UNUSED_LOCAL(x) (void)x
-
 #endif  // CEF_INCLUDE_BASE_CEF_COMPILER_SPECIFIC_H_