linker: do not copy instructions when there is no reference in flattenInstructions
#1517
| Job | Run time |
|---|---|
| 18s | |
| 3m 3s | |
| 3m 17s | |
| 1m 52s | |
| 1m 8s | |
| 50s | |
| 1m 16s | |
| 1m 17s | |
| 1m 17s | |
| 1m 53s | |
| 1m 20s | |
| 1m 51s | |
| 1m 8s | |
| 1m 15s | |
| 21m 45s |