[StandardInstrumentations] Add option to dump IR to a file on crash

[StandardInstrumentations] Add option to dump IR to a file on crash

We already have -print-on-crash which dumps the IR to stderr on a crash, but it's more useful to dump to a file.

Introduce -print-on-crash-path to dump the IR to a file.

Making -print-on-crash a string option is confusing if you only pass -print-on-crash and it swallows up the next command line arg, which is why this is a new option.

Perhaps we could retire the dump to stderr version if people don't use it, but not sure how much people find that useful.

Reviewed By: jamieschmeiser

Differential Revision: https://reviews.llvm.org/D151170