use __has_builtin to detect available intrinsics (#846)
#296
| Job | Run time |
|---|---|
| 30m 13s | |
| 14m 1s | |
| 19m 37s | |
| 8m 16s | |
| 10m 27s | |
| 11m 29s | |
| 14m 19s | |
| 9m 9s | |
| 12m 20s | |
| 8m 22s | |
| 11m 50s | |
| 14m 48s | |
| 11m 54s | |
| 14m 22s | |
| 13m 36s | |
| 3h 24m 43s |