C major change: skip redefinition of internal XS CVs

Internal XS xsubs are already booted in the perl_parse step.
When we encounter them we set new GPs for those, which was a problem on Windows
where we cannot declare and boot the said XS functions (not exported).
We rather keep the old GV, GP and CV.

Conflicts:
	Changes
C: fix issue #125, Can't locate object method "bootstrap_inherit" via package "DynaLoader"

Remove premature GV optimization not to store in_static_core() symbols,
because there are some mixed PP/XS core CV's which need to be saved.
Such as all DynaLoader.pm symbols and functions.
_autovivification: Perl_ck_null is not exported, use PL_check[0] instead

Detected on Windows

Fixed Conflicts:
	C.xs