build: add quotes around CMAKE_GENERATOR variable
#570
| Job | Run time |
|---|---|
| 8m 34s | |
| 3m 13s | |
| 2m 36s | |
| 2m 25s | |
| 14m 38s | |
| 1m 5s | |
| 6m 57s | |
| 15m 44s | |
| 1m 36s | |
| 7m 4s | |
| 3m 32s | |
| 3m 9s | |
| 12m 42s | |
| 5m 53s | |
| 1m 41s | |
| 6m 52s | |
| 3m 14s | |
| 7m 26s | |
| 3m 2s | |
| 13m 14s | |
| 6m 25s | |
| 2h 11m 2s |