configure: make HWLOC_VERSION available everywhere, even in embedded

VERSION is only available in standalone.
Move the extracting of VERSION to HWLOC_SETUP_CORE,
and update PACKAGE_VERSION accordingly later.
Use HWLOC_VERSION instead of VERSION everywhere in the code
core: add the HWLOC_VERSION string to error messages

Will help find the corresponding line in the source code, etc.
core: export hwloc__object_cpusets_compare_first()
core: insert_object_by_parent() doesn't need to check children order, only XML does

Most use cases of insert_object_by_parent() are just inserting I/O and Misc,
no cpuset ordering there.
Out-of-order when duplicating would require a fix in the source topology,
not at duplicate/insert time.
XML is the only case when out-of-order insert_by_parent() can really occur,
move the warning to the XML code, and improve the error message.