expander: repair literal syntax in test position of if

Fix mishandling of an expanded `if` where the test position is a
syntax object. The expander's compiler pass from expanded objects to
linkets knows that the syntax object isn't useful, but it tried to be
helpful by preserving the syntax object's content as quoted --- and
that content turns out not to be available, so the syntax object was
replaced by #f, instead.

Closes #3436

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

@@ -82,6 +82,9 @@
 (syntax-test #'(+ 3 . 4))
 (syntax-test #'(apply + 1 . 2))
 
+(test 'ok 'check-literal-quote-syntax-as-test (if (quote-syntax yes) 'ok 'bug!))
+(test 'ok2 'check-literal-quote-syntax-as-test (if (quote-syntax #f) 'ok2 'bug!))
+
 (test 8 (lambda (x) (+ x x)) 4)
 (define reverse-subtract
   (lambda (x y) (- y x)))

racket/src/bc/src/startup.inc

@@ -31623,7 +31623,7 @@ static const char *startup_source =
 "(compile-quote-syntax"
 "(parsed-quote-syntax-datum p_0)"
 " cctx_0)"
-"(correlate~ s_0(list 'quote(syntax->datum$1 s_0)))))"
+"(correlate~ s_0 ''syntax)))"
 "(if(parsed-#%variable-reference? p_0)"
 "(let-values()"
 "(let-values(((id_0)"

racket/src/cs/schemified/expander.scm

@@ -38609,10 +38609,7 @@
                                               (compile-quote-syntax
                                                (parsed-quote-syntax-datum p3_0)
                                                cctx4_0)
-                                              (let ((s-exp_0
-                                                     (list
-                                                      'quote
-                                                      (syntax->datum$1 s_0))))
+                                              (let ((s-exp_0 ''syntax))
                                                 s-exp_0))
                                             (if (|parsed-#%variable-reference?|
                                                  p3_0)

racket/src/expander/compile/expr.rkt

@@ -106,7 +106,9 @@
      [(parsed-quote-syntax? p)
       (if result-used?
           (compile-quote-syntax (parsed-quote-syntax-datum p) cctx)
-          (correlate~ s `(quote ,(syntax->datum s))))]
+          ;; Note: the datum form of `s` has probably been pruned away,
+          ;; so don't try to use it here:
+          (correlate~ s `(quote syntax)))]
      [(parsed-#%variable-reference? p)
       (define id (parsed-#%variable-reference-id p))
       (correlate~ s