runtime: default GOMAXPROCS to NumCPU(), not 1

See golang.org/s/go15gomaxprocs for details.

Change-Id: I8de5df34fa01d31d78f0194ec78a2474c281243c
Reviewed-on: https://go-review.googlesource.com/10668Reviewed-by: Rob Pike <r@golang.org>

src/runtime/proc1.go

@@ -62,7 +62,7 @@ func schedinit() {
 	gcinit()
 
 	sched.lastpoll = uint64(nanotime())
-	procs := 1
+	procs := int(ncpu)
 	if n := atoi(gogetenv("GOMAXPROCS")); n > 0 {
 		if n > _MaxGomaxprocs {
 			n = _MaxGomaxprocs