runtime: fix netbsd build

I've placed net.runtime_Semacquire into netpoll.goc,
but netbsd does not yet use netpoll.goc.

R=golang-dev, bradfitz, iant
CC=golang-dev
https://golang.org/cl/12699045

src/pkg/runtime/netpoll.goc

@@ -206,14 +206,6 @@ func runtime_pollUnblock(pd *PollDesc) {
 		runtime·ready(wg);
 }
 
-func runtime_Semacquire(addr *uint32) {
-	runtime·semacquire(addr, true);
-}
-
-func runtime_Semrelease(addr *uint32) {
-	runtime·semrelease(addr);
-}
-
 uintptr
 runtime·netpollfd(PollDesc *pd)
 {

src/pkg/runtime/sema.goc

@@ -182,6 +182,17 @@ runtime·semrelease(uint32 volatile *addr)
 	}
 }
 
+// TODO(dvyukov): move to netpoll.goc once it's used by all OSes.
+void net·runtime_Semacquire(uint32 *addr)
+{
+	runtime·semacquire(addr, true);
+}
+
+void net·runtime_Semrelease(uint32 *addr)
+{
+	runtime·semrelease(addr);
+}
+
 func runtime_Semacquire(addr *uint32) {
 	runtime·semacquire(addr, true);
 }