[clang] [llvm] [polly] [polly][ScheduleOptimizer] Fix long compile time(hang) reported in polly (PR #75141)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

The isl_options_set_on_error thing still seems like an issue; there's a path to restore on_error, but it doesn't run if the quota is hit.

Do we actually need to explicitly check hasQuotaExceeded() at all?  If there's an error, the schedule should be null, and there's already a check for `if (Schedule.is_null())`.

https://github.com/llvm/llvm-project/pull/75141