+ WASI threads: define FPC_WASM_WORKER_THREADS_CAN_WAIT. It is actually true in

  all known cases (command line WASI or browser).

rtl/wasi/systhrd.inc

@@ -20,7 +20,7 @@
 {$endif FPC_WASM_THREADS}
 
 {$DEFINE FPC_WASM_MAIN_THREAD_CAN_WAIT}
-{$UNDEF FPC_WASM_WORKER_THREADS_CAN_WAIT}
+{$DEFINE FPC_WASM_WORKER_THREADS_CAN_WAIT}
 
 {//$DEFINE DEBUGWASMTHREADS}