[compiler] Make --debug-code the default in debug builds.

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 534 matching lines @@
 DEFINE_INT(type_info_threshold, 25,
            "percentage of ICs that must have type info to allow optimization")
 DEFINE_INT(generic_ic_threshold, 30,
            "max percentage of megamorphic/generic ICs to allow optimization")
 DEFINE_INT(self_opt_count, 130, "call count before self-optimization")
 
 DEFINE_BOOL(trace_opt_verbose, false, "extra verbose compilation tracing")
 DEFINE_IMPLICATION(trace_opt_verbose, trace_opt)
 
 // assembler-ia32.cc / assembler-arm.cc / assembler-x64.cc
-DEFINE_BOOL(debug_code, false, "generate extra code (assertions) for debugging")
+DEFINE_BOOL(debug_code, DEBUG_BOOL,
+            "generate extra code (assertions) for debugging")
 DEFINE_BOOL(code_comments, false, "emit comments in code disassembly")
 DEFINE_BOOL(enable_sse3, true, "enable use of SSE3 instructions if available")
 DEFINE_BOOL(enable_ssse3, true, "enable use of SSSE3 instructions if available")
 DEFINE_BOOL(enable_sse4_1, true,
             "enable use of SSE4.1 instructions if available")
 DEFINE_BOOL(enable_sahf, true,
             "enable use of SAHF instruction if available (X64 only)")
 DEFINE_BOOL(enable_avx, true, "enable use of AVX instructions if available")
 DEFINE_BOOL(enable_fma3, true, "enable use of FMA3 instructions if available")
 DEFINE_BOOL(enable_bmi1, true, "enable use of BMI1 instructions if available")
@@ skipping 672 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