runtime: resolve latent function type TODO

This was left over from the C->Go transition.

Change-Id: I52494af3d49a388dc45b57210ba68292ae01cf84
Reviewed-on: https://go-review.googlesource.com/c/go/+/176897
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/proc.go

@@ -295,7 +295,7 @@ func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason w
 		throw("gopark: bad g status")
 	}
 	mp.waitlock = lock
-	mp.waitunlockf = *(*unsafe.Pointer)(unsafe.Pointer(&unlockf))
+	mp.waitunlockf = unlockf
 	gp.waitreason = reason
 	mp.waittraceev = traceEv
 	mp.waittraceskip = traceskip
@@ -2595,8 +2595,7 @@ func park_m(gp *g) {
 	casgstatus(gp, _Grunning, _Gwaiting)
 	dropg()
 
-	if _g_.m.waitunlockf != nil {
-		fn := *(*func(*g, unsafe.Pointer) bool)(unsafe.Pointer(&_g_.m.waitunlockf))
+	if fn := _g_.m.waitunlockf; fn != nil {
 		ok := fn(gp, _g_.m.waitlock)
 		_g_.m.waitunlockf = nil
 		_g_.m.waitlock = nil

src/runtime/runtime2.go

@@ -491,11 +491,11 @@ type m struct {
 	schedlink     muintptr
 	mcache        *mcache
 	lockedg       guintptr
-	createstack   [32]uintptr    // stack that created this thread.
-	lockedExt     uint32         // tracking for external LockOSThread
-	lockedInt     uint32         // tracking for internal lockOSThread
-	nextwaitm     muintptr       // next m waiting for lock
-	waitunlockf   unsafe.Pointer // todo go func(*g, unsafe.pointer) bool
+	createstack   [32]uintptr // stack that created this thread.
+	lockedExt     uint32      // tracking for external LockOSThread
+	lockedInt     uint32      // tracking for internal lockOSThread
+	nextwaitm     muintptr    // next m waiting for lock
+	waitunlockf   func(*g, unsafe.Pointer) bool
 	waitlock      unsafe.Pointer
 	waittraceev   byte
 	waittraceskip int