const runtime.gcForceBlockMode

3 uses

	runtime (current package)
		mgc.go#L583: 	gcForceBlockMode               // stop-the-world GC now and STW sweep (forced by user)
		mgc.go#L697: 		mode = gcForceBlockMode
		mgc.go#L1735: 	if !concurrentSweep || mode == gcForceBlockMode {