ffi added compile-time attrs leaks

[rurban]

With GH #22, see t/op/svleak.t: tests

+sub:a{}
extern sub labs ();
sub labs () :native("c");
sub ffiabs () :native :symbol("labs");

=>

not ok 91 - anon subs with invalid attributes # TODO compile-time attrs leaks
# Failed test 91 - anon subs with invalid attributes at t/op/svleak.t line 31
#      got "1"
# expected <= "0"
not ok 92 - extern sub # TODO compile-time attrs leaks
# Failed test 92 - extern sub at t/op/svleak.t line 31
#      got "1"
# expected <= "0"
not ok 93 - sub :native("c") # TODO compile-time attrs leaks
# Failed test 93 - sub :native("c") at t/op/svleak.t line 31
#      got "5"
# expected <= "0"
not ok 94 - extern sub :symbol("name") # TODO compile-time attrs leaks
# Failed test 94 - extern sub :symbol("name") at t/op/svleak.t line 31
#      got "5"
# expected <= "0"