still fixing host most-fooative-fixnum leaks

the two substantive fixes here (adding tasteful sb!xc package
prefixes) make src/code/late-extensions compile identically
under clisp and sbcl host compilers.
plug one more xc leak

using the results of INTERSECTION / SET-DIFFERENCE in macros can
lead to differences in fasls, for example from recording source.
Deterministify using SORT.