runtime: make goroutine stack size larger on sparc64
runtime: make goroutine stack size larger on sparc64

SPARC64 has a lot of stack frame overhead. Smaller stacks cause a
stack split in the runtime before we are prepared to deal with stack
splits.

4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go