[PATCH] [lsan] Enable i386 support. Also rework the lit test configs.

[Sergey Matveev]

  One option: on i386, test only for false positives.

  This shouldn't be hard to do with substitutions: instead of

  // RUN: ...

  we can have

  /// RUN: %FALSE_NEGATIVE_TEST ...

  %FALSE_NEGATIVE TEST is expanded to "true &&" on x86_64 and to "false &&" on i386

http://llvm-reviews.chandlerc.com/D1015