Add flags -Rpass-missed and -Rpass-analysis.

Summary:
These two flags are in the same family as -Rpass, but are used in
different situations.

-Rpass-missed is used by optimizers to inform the user when they tried
to apply an optimization but couldn't (or wouldn't).

-Rpass-analysis is used by optimizers to report analysis results back
to the user (e.g., why the transformation could not be applied).

Depends on D3682.

Reviewers: rsmith

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D3683