out_stackdriver: use new 'pthread' wrapper in header
#include <fluent-bit/flb_output.h>
#include <fluent-bit/flb_oauth2.h>
#include <fluent-bit/flb_sds.h>
-#include <pthread.h>
+#include <fluent-bit/flb_pthread.h>
/* refresh token every 50 minutes */
#define FLB_STD_TOKEN_REFRESH 3000
