Add `core:flags` to `examples/all`

examples/all/all_main.odin

@@ -121,6 +121,7 @@ import edit             "core:text/edit"
 import thread           "core:thread"
 import time             "core:time"
 import datetime         "core:time/datetime"
+import flags            "core:flags"
 
 import sysinfo          "core:sys/info"