vm_insnhelper.c: USE_FLONUM is always defined

This changeset should fix the 32bit failures.
See also: https://travis-ci.org/ruby/ruby/jobs/472855470


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66601 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

vm_insnhelper.c

@@ -1406,7 +1406,7 @@ FIXNUM_2_P(VALUE a, VALUE b)
 static bool
 FLONUM_2_P(VALUE a, VALUE b)
 {
-#ifdef USE_FLONUM
+#if USE_FLONUM
     /* FLONUM_P(a) && FLONUM_P(b)
      * == ((a & 3) == 2) && ((b & 3) == 2)
      * == ! ((a ^ 2) | (b ^ 2) & 3)