Revert "Skip calling jit_exec on Wasm"

This reverts commit e80752f.

RJIT and YJIT are never enabled on Wasm.  When both are disabled,
`jit_exec` is defined to return `Qundef` constantly, and is optimized
away.

vm.c

@@ -2336,7 +2336,9 @@ vm_exec_bottom_main(void *context)
     struct rb_vm_exec_context *ctx = (struct rb_vm_exec_context *)context;
 
     ctx->state = TAG_NONE;
-    ctx->result = vm_exec_core(ctx->ec);
+    if (UNDEF_P(ctx->result = jit_exec(ctx->ec))) {
+        ctx->result = vm_exec_core(ctx->ec);
+    }
     vm_exec_enter_vm_loop(ctx->ec, ctx, ctx->tag, true);
 }