runtime: convert lock*.c to Go
LGTM=r, iant
R=golang-codereviews, r, iant
CC=dvyukov, golang-codereviews, khr
https://golang.org/cl/139930043
diff --git a/src/pkg/runtime/os_dragonfly.go b/src/pkg/runtime/os_dragonfly.go
index ec7ddef..3e7fc8d 100644
--- a/src/pkg/runtime/os_dragonfly.go
+++ b/src/pkg/runtime/os_dragonfly.go
@@ -19,3 +19,5 @@
func closeonexec(fd int32)
func sys_umtx_sleep(addr unsafe.Pointer, val, timeout int32) int32
func sys_umtx_wakeup(addr unsafe.Pointer, val int32) int32
+
+const stackSystem = 0
