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

tools/jsfunfuzz/fuzz-harness.sh

 #!/bin/bash
 # Copyright 2016 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.
 
 # A simple harness that downloads and runs 'jsfunfuzz' against d8. This
 # takes a long time because it runs many iterations and is intended for
 # automated usage. The package containing 'jsfunfuzz' can be found as an
 # attachment to this bug:
 # https://bugzilla.mozilla.org/show_bug.cgi?id=jsfunfuzz
@@ skipping 47 matching lines @@
 -    while True:
 +    while iteration < 100:
          iteration += 1
          logfilename = "w%d" % iteration
          one_timed_run(logfilename)
 EOF
   fi
 
 fi
 
-flags='--debug-code --expose-gc --verify-gc'
+flags='--expose-gc --verify-gc'
 python -u "$jsfunfuzz_dir/jsfunfuzz/multi_timed_run.py" 300 \
     "$d8" $flags "$jsfunfuzz_dir/jsfunfuzz/jsfunfuzz.js"
 exit_code=$(cat w* | grep " looking good" -c)
 exit_code=$((100-exit_code))
 
 if [ -n "$2" ]; then
   archive="$2"
 else
   archive=fuzz-results-$(date +%Y%m%d%H%M%S).tar.bz2
 fi
 echo "Creating archive $archive"
 tar -cjf $archive err-* w*
 rm -f err-* w*
 
 echo "Total failures: $exit_code"
 exit $exit_code