[MFProperties] Introduce a FailedISel property.

[MFProperties] Introduce a FailedISel property.

This is used to communicate that the instruction selection pipeline
failed at some point.
Another way to achieve that would be to have some kind of conditional
scheduling in the PassManager, such that we only schedule a pass based
on the success/failure of another one. The property approach has the
advantage of being lightweight and solve the problem at stake.

llvm-svn: 279885