bytecode optimizer: allow inline of unsafe-undefined

Restores some function inlining that was lost by the change to
optional-argument expansion.

pkgs/racket-test-core/tests/racket/optimize.rktl

@@ -4319,6 +4319,23 @@
 (test-comp '(lambda () (bytes=? #"123" #"456"))
            '(lambda () #f))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Check inlining with optional arguments
+
+(test-comp '(lambda (x)
+              (define (f z [y 2])
+                (+ z y))
+              (f x))
+           '(lambda (x)
+              (+ x 2)))
+
+(test-comp '(lambda (x)
+              (define (f z [y (+ 1 1)])
+                (+ z y))
+              (f x))
+           '(lambda (x)
+              (+ x 2)))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Check that the type information is shifted in the
 ;; right direction while inlining.

racket/src/racket/src/optimize.c

@@ -2269,6 +2269,7 @@ int scheme_ir_duplicate_ok(Scheme_Object *fb, int cross_linklet)
 {
   return (SCHEME_VOIDP(fb)
           || SAME_OBJ(fb, scheme_true)
+          || SAME_OBJ(fb, scheme_undefined)
           || SCHEME_FALSEP(fb)
           || (SCHEME_SYMBOLP(fb) 
               && (!cross_linklet || (!SCHEME_SYM_WEIRDP(fb)