The _GLIBCXX_DEBUG macro is now set by default for Linux Debug builds
and can be disabled using the disable_glibcxx_debug=1 setting
(compatible with Chrome).  This will help us catch problems earlier.

BUG=v8:3638
LOG=n

Review URL: https://codereview.chromium.org/946283003

Cr-Commit-Position: refs/heads/master@{#26790}