DM: make --verbose send the vlog to stderr.

See if this works out for you?
I've just turned off --verbose on the bots, so this ought to be safe now.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1808203004

Review URL: https://codereview.chromium.org/1808203004
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 24c4799..1302463 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -1311,7 +1311,9 @@
 int dm_main() {
     setup_crash_handler();
 
-    if (!FLAGS_writePath.isEmpty()) {
+    if (FLAGS_verbose) {
+        gVLog = stderr;
+    } else if (!FLAGS_writePath.isEmpty()) {
         sk_mkdir(FLAGS_writePath[0]);
         gVLog = freopen(SkOSPath::Join(FLAGS_writePath[0], "verbose.log").c_str(), "w", stderr);
     }