[isl++] abort() on assertion violation.
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>
Differential Revision: https://reviews.llvm.org/D45171
git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@330467 91177308-0d34-0410-b5e6-96231b3b80d8