syscall: add yet more TestGetfsstat debugging

Updates #16937

Change-Id: I98aa203176f8f2ca2fcca6e334a65bc60d6f824d
Reviewed-on: https://go-review.googlesource.com/28535Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/syscall_bsd_test.go

@@ -7,6 +7,7 @@
 package syscall_test
 
 import (
+	"os/exec"
 	"syscall"
 	"testing"
 )
@@ -33,4 +34,15 @@ func TestGetfsstat(t *testing.T) {
 			t.Errorf("index %v is an empty Statfs_t struct", i)
 		}
 	}
+	if t.Failed() {
+		for i, stat := range data {
+			t.Logf("data[%v] = %+v", i, stat)
+		}
+		mount, err := exec.Command("mount").CombinedOutput()
+		if err != nil {
+			t.Logf("mount: %v\n%s", err, mount)
+		} else {
+			t.Logf("mount: %s", mount)
+		}
+	}
 }