include: speed up compat header generation

include: speed up compat header generation

Recent additions to xlat.lst have apparently resulted in Python's
garbage collection getting in the way: I would guess that so far it
managed to re-use previously compiled regular expressions, but with the
higher number of them now can't anymore (at least with default
settings). Do the compilation explicitly. While at it, combine the two
lists, and avoid using re.subn() when re.sub() suffices.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>