runtime: distinguish semaphore wait from sync.Cond.Wait

Updates #24362.

Change-Id: Ided1ab31792f05d9d7a86f17c1bcbd9e9b80052c
Reviewed-on: https://go-review.googlesource.com/102606
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/sema.go

@@ -507,7 +507,7 @@ func notifyListWait(l *notifyList, t uint32) {
 		l.tail.next = s
 	}
 	l.tail = s
-	goparkunlock(&l.lock, "semacquire", traceEvGoBlockCond, 3)
+	goparkunlock(&l.lock, "sync.Cond.Wait", traceEvGoBlockCond, 3)
 	if t0 != 0 {
 		blockevent(s.releasetime-t0, 2)
 	}