[opt-viewer] Teach optrecord.py about !Failure tags

WarnMissedTransforms.cpp produces remarks that use !Failure tags.

These weren't supported in optrecord.py, so if you encountered one in any of
the tools, the tool would crash.

Add them as a type of missed optimization.

Differential Revision: https://reviews.llvm.org/D59895

llvm-svn: 357110