De-break round-trip of some circular structures

The fix[^1] to fix .perl.EVAL roundtripping of Array and Hash circular
accidentally broke compilation of .perl of all the other types of structures.

Even though they're still broken in the sense that their EVAL does not
produce the correct values, this commit at least unbreaks their compilation.

[1] 67aeefacf5fb9c35189bcc70

src/core/Mu.pm

@@ -508,15 +508,17 @@ my class Mu { # declared in BOOTSTRAP
             my str $WHICH = nqp::unbox_s(self.WHICH);
             if nqp::existskey(sems,$WHICH) && nqp::atkey(sems,$WHICH) {
                 nqp::bindkey(sems,$WHICH,2);
-                "{$sigil}{$id}_{nqp::objectid(SELF)}";
+                $sigil x nqp::isne_s($sigil, '\\') ~ "{$id}_{nqp::objectid(SELF)}";
             }
             else {
                 nqp::bindkey(sems,$WHICH,1);
                 my $result := $perl(|%named);
                 my int $value = nqp::atkey(sems,$WHICH);
                 nqp::deletekey(sems,$WHICH);
                 $value == 2
-                  ?? "((my {$sigil}{$id}_{nqp::objectid(SELF)}) = $result)"
+                  ?? nqp::iseq_s($sigil, '\\')
+                    ??  "(my {$sigil}{$id}_{nqp::objectid(SELF)} = $result)"
+                    !! "((my {$sigil}{$id}_{nqp::objectid(SELF)}) = $result)"
                   !! $result
             }
         }