Disable core_bool_support if builtin is_bool is not defineed

Author: charsbar

t/e02_bool.t

@@ -20,6 +20,7 @@ my $not_not_a_number_is_a_number = (
 
 my $core_bool_support = JSON->backend->can("CORE_BOOL") && JSON->backend->CORE_BOOL ? 1 : 0;
 $core_bool_support = 1 if $json->backend->isa('Cpanel::JSON::XS') && $json->backend->VERSION >= version->parse(4.38);
+$core_bool_support = 0 unless defined &builtin::is_bool;
 
 is($json->encode([!1]), $core_bool_support ? '[false]' : '[""]');
 if ($not_not_a_number_is_a_number) {