swift234

SIL GlobalOpt pass: hoist init calls to the outer preheader.

This seems to consistently improve two benchmarks.
| key         |     tot0 |     tot1 |     tot2 |     opt0 |     opt1 |     opt2 |  delta | speedup |
| Ackermann   |  4036.00 |  4016.00 |  3941.00 |  3785.00 |  3843.00 |  3827.00 | 156.00 |    4.1% |
| LinkedList  |  1551.00 |  1606.00 |  1540.00 |  1523.00 |  1531.00 |  1516.00 |  24.00 |    1.6% |

Swift SVN r19571