Define DEBUG for v8_optimized_debug=2

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 678 matching lines @@
 // Debug only flags
 //
 #undef FLAG
 #ifdef DEBUG
 #define FLAG FLAG_FULL
 #else
 #define FLAG FLAG_READONLY
 #endif
 
 // checks.cc
+#ifndef OPTIMIZED_DEBUG
 DEFINE_bool(enable_slow_asserts, false,
             "enable asserts that are slow to execute")
+#endif
 
 // codegen-ia32.cc / codegen-arm.cc / macro-assembler-*.cc
 DEFINE_bool(print_source, false, "pretty print source code")
 DEFINE_bool(print_builtin_source, false,
             "pretty print source code for builtins")
 DEFINE_bool(print_ast, false, "print source AST")
 DEFINE_bool(print_builtin_ast, false, "print source AST for builtins")
 DEFINE_string(stop_at, "", "function name where to insert a breakpoint")
 DEFINE_bool(trap_on_abort, false, "replace aborts by breakpoints")
 
@@ skipping 166 matching lines @@
 #undef DEFINE_ALIAS_float
 #undef DEFINE_ALIAS_args
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA