[dev.power64] all: merge default into dev.power64

Trivial merge except for src/runtime/asm_power64x.s and
src/runtime/signal_power64x.c

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/168950044

src/cmd/objdump/objdump_test.go

@@ -147,7 +147,7 @@ var x86Need = []string{
 var armNeed = []string{
 	"fmthello.go:6",
 	"TEXT main.main(SB)",
-	"B.LS main.main(SB)",
+	//"B.LS main.main(SB)", // TODO(rsc): restore; golang.org/issue/9021
 	"BL fmt.Println(SB)",
 	"RET",
 }