Use correct exclusion comment

Author: oli-obk

src/test/run-pass/invalid_const_promotion.rs

@@ -8,7 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// ignore-wasm
+// ignore-wasm32
+// ignore-emscripten
 
 #![feature(const_fn)]
 #![allow(const_err)]