Don't call exit() after __debugbreak() on release builds.

This CL optimizes code for debugging as opposed to for someone who attaches a
debugger and goes beyond a CHECK without realizing it. Debugging a release
build is already hard, especially on 64-bit builds.

BUG=408820
R=wfh@chromium.org

Review URL: https://codereview.chromium.org/759283005

Cr-Commit-Position: refs/heads/master@{#306871}
4 files changed