ggml : init time on first ggml_init() call

ggml.c

@@ -2748,6 +2748,9 @@ struct ggml_context * ggml_init(struct ggml_init_params params) {
     static bool is_first_call = true;
 
     if (is_first_call) {
+        // initialize time system (required on Windows)
+        ggml_time_init();
+
         // initialize GELU, SILU and EXP F32 tables
         {
             const uint64_t t_start = ggml_time_us(); UNUSED(t_start);