runtime,sync: Convert procPin and procUnpin functions to Go.

LGTM=dvyukov
R=golang-codereviews, dvyukov
CC=golang-codereviews, khr
https://golang.org/cl/132880043

src/pkg/runtime/proc.c

@@ -3292,3 +3292,23 @@ haveexperiment(int8 *name)
 	}
 	return 0;
 }
+
+#pragma textflag NOSPLIT
+void
+sync·runtime_procPin(intptr p)
+{
+	M *mp;
+
+	mp = g->m;
+	// Disable preemption.
+	mp->locks++;
+	p = mp->p->id;
+	FLUSH(&p);
+}
+
+#pragma textflag NOSPLIT
+void
+sync·runtime_procUnpin()
+{
+	g->m->locks--;
+}

src/pkg/runtime/runtime1.goc

@@ -114,15 +114,3 @@ func runtime∕pprof·runtime_cyclesPerSecond() (res int64) {
 	res = runtime·tickspersecond();
 }
 
-func sync·runtime_procPin() (p int) {
-	M *mp;
-
-	mp = g->m;
-	// Disable preemption.
-	mp->locks++;
-	p = mp->p->id;
-}
-
-func sync·runtime_procUnpin() {
-	g->m->locks--;
-}