C new-cog: unstatic readonly and certain internal XSLoader pvs

Our own implementation of evaled XSLoader::load needs dynamic strings.

Still failing -O3 tests: 12(new), 75,91,95,125,143,152,159,166(new),185,188
so it fixed: 15,27,29,41-45,49,68,90,103,150
and broke: 12,166