Two changes:
  - In ReportBootstrappingException, if all we have is a string, it seems
    better to print that than nothing.
  - In Factory::NewError, there's no use trying to call into the builtins if
    compilation of the builtins is causing the exception (this currently
    results in a cryptic segfault if we trigger, say, a ReferenceError when
    executing builtins script during bootstrapping).

Review URL: https://codereview.chromium.org/1158013003

Cr-Commit-Position: refs/heads/master@{#28912}