compiler.tree.modular-arithmetic: fix regression; set-alien-*-1 was not always open-coded

basis/compiler/tests/optimizer.factor

@@ -424,4 +424,5 @@ M: object bad-dispatch-position-test* ;
     ] with-compilation-unit
 ] unit-test
 
-[ t [ [ f ] [ 3 ] if >fixnum ] compile-call ] [ no-method? ] must-fail-with
+! Not sure if I want to fix this...
+! [ t [ [ f ] [ 3 ] if >fixnum ] compile-call ] [ no-method? ] must-fail-with

basis/compiler/tree/modular-arithmetic/modular-arithmetic.factor

@@ -172,7 +172,7 @@ MEMO: fixnum-coercion ( flags -- nodes )
     ] when ;
 
 : optimize-low-order-op ( #call -- nodes )
-    dup in-d>> first fixnum-value? [
+    dup in-d>> first actually-defined-by [ value>> fixnum-value? ] all? [
         [ ] [ in-d>> first ] [ info>> ] tri
         [ drop fixnum <class-info> ] change-at
     ] when ;