flush after every print in windows

gm/gm_expectations.cpp

Index: gm/gm_expectations.cpp
diff --git a/gm/gm_expectations.cpp b/gm/gm_expectations.cpp
index 7d6ccf64642817f173cef29cc7ec381c412fcea1..63aa638aac58de2ff952666041e68601a40e76b8 100644
--- a/gm/gm_expectations.cpp
+++ b/gm/gm_expectations.cpp
@@ -34,6 +34,11 @@ namespace skiagm {
         va_start(args, format);
         fprintf(stream, "GM: ");
         vfprintf(stream, format, args);
+#ifdef SK_BUILD_FOR_WIN
+        if (stderr == stream || stdout == stream) {
+            fflush(stream);
+        }
+#endif
         va_end(args);
     }