[Wasm] Mute codegen box tests

compiler/testData/codegen/box/specialBuiltins/throwableComplex.kt

@@ -1,3 +1,5 @@
+// DONT_TARGET_EXACT_BACKEND: WASM
+// WASM_MUTE_REASON: EXCEPTIONS_NOT_IMPLEMENTED
 // Super calls to Throwable properties are not supported
 // IGNORE_BACKEND: JS_IR
 // IGNORE_BACKEND: JS_IR_ES6
@@ -43,4 +45,4 @@ fun check(t: Throwable, msg: String) {
         val m = if (c != null) t.message!! + c.message!! else t.message!!
         if (m != msg) throw AssertionError(m)
     }
-}
+}