runtime/race: memory leak in race runtime

[dvyukov]

The leak was reported internally on a sever canary that runs for days.
After a day server consumes 5.6GB, after 6 days -- 12.2GB.
The leak is exposed by the following benchmark:

func BenchmarkStackLeak(b *testing.B) {
    done := make(chan bool, 1)
    for i := 0; i < b.N; i++ {
        go func() {
            growStack(rand.Intn(100))
            done <- true
        }()
        <-done
    }
}

func growStack(i int) {
    if i == 0 {
        return
    }
    growStack(i - 1)
}

The leak is fixed upstream in :
http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/tsan/rtl/tsan_rtl_thread.cc?view=diff&r1=276102&r2=276103&pathrev=276103

[gopherbot]

CL https://golang.org/cl/25091 mentions this issue.

[dvyukov]

The change is submitted. The is not autoclosed for some reason. Closing.

[dvyukov]

Reopened in case this needs to be merged into 1.7.

[bradfitz]

@dvyukov, we use separate bugs for master fixes vs branch cherry-picks now.