[dev.ssa] cmd/compile/internal/ssa/gen: enclose rules' code in a for loop
* Enclose each rule's code in a for with no condition
* The loop is ran at most once because it's always terminated by a return.
* Use break when matching condition fails
* Drop rule hashes
* Shaves about 3 lines of code per rule
The binary size is not afected.
Change-Id: I27c3e40dc8cae98dcd50739342dc38db2ef9c247
Reviewed-on: https://go-review.googlesource.com/19220 Reviewed-by: Keith Randall <khr@golang.org>