Previously `report_fatal_error` is used for reporting something goes
wrong in the backend, but this is confusing because `report_fatal_error`
basically means there are something unexpected & crashed in the backend.
So, turn this "crash" into an elegant error reporting. After this patch,
clang can diagnose it:
bpf-crash.c:4:30: error: Invalid usage of the XADD return value
4 | u32 next_event_id() { return __sync_fetch_and_add(&GLOBAL_EVENT_ID,
1); }
| ^
1 error generated.
c6486633d2