Fix mac build

src/core/lib/surface/api_trace.c

@@ -31,6 +31,7 @@
  *
  */
 
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/surface/api_trace.h"
 
-grpc_tracer_flag grpc_api_trace;
+grpc_tracer_flag grpc_api_trace = GRPC_TRACER_INITIALIZER(false);