Fix regression of 88603655

Fix regression of 88603655

The XHTML entries were added in the wrong field, if they are given we need
extra xhtml requires. The order is inconsistent, there are discussions on the
list about that but for now I'll use the existing order to fix the export tests.

The format of the lib/symbols file does not support "" for empty strings.
One would have to use x for fields that are not set (this is a hack), but
actually we know how to fill the extra field.

(cherry-pick of commit 338cef2a)