runtime: fix netbsd, windows build

TBR=golang-dev
CC=golang-dev
https://golang.org/cl/7539043

src/pkg/runtime/rt0_netbsd_amd64.s

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-TEXT _rt0_amd64_openbsd(SB),7,$-8
+TEXT _rt0_amd64_netbsd(SB),7,$-8
 	LEAQ	8(SP), SI // argv
 	MOVQ	0(SP), DI // argc
 	MOVQ	$main(SB), AX

src/pkg/runtime/rt0_windows_amd64.s

@@ -4,7 +4,7 @@
 
 #include "zasm_GOOS_GOARCH.h"
 
-TEXT _rt0_amd64_darwin(SB),7,$-8
+TEXT _rt0_amd64_windows(SB),7,$-8
 	LEAQ	8(SP), SI // argv
 	MOVQ	0(SP), DI // argc
 	MOVQ	$main(SB), AX