Before this patch, ISL_ASSERT only printed an error message to stderr. This can be easily missed if the program continues or just fails later. To fail-early and help error diagnostics (e.g. using bugpoint), call abort() when an assertion does not hold.
I seem to just have forgotten to add this abort() when I originally proposed the ISL_ASSERT macro.
Suggested-By: Eli Friedman <efriedma@codeaurora.org>