Fix windows portability

test/core/transport/bdp_estimator_test.cc

@@ -37,9 +37,11 @@ namespace {
 int g_clock = 0;
 
 gpr_timespec fake_gpr_now(gpr_clock_type clock_type) {
-  return (gpr_timespec){
+  gpr_timespec ts;
-      .tv_sec = g_clock, .tv_nsec = 0, .clock_type = clock_type,
+  ts.tv_sec = g_clock;
-  };
+  ts.tv_nsec = 0;
+  ts.clock_type = clock_type;
+  return ts;
 }
 
 void inc_time(void) { g_clock += 30; }