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 newGP replacement for windows

proto.h still defines Perl_newGP as being imported, despite its embed.fnc flags.
So we get _imp_Perl_newGP not being found errors when linking with the perl516 importlib.

Fixed Conflicts:
	lib/B/C.pm
C: fix #126 Do not reset existing CVs

Do not reset the GvCV of already booted core XS functions.
Backpatch the init section for those few functions (re, mro, UNIVERSAL, ...)
C: win move share_hek above, improve windows $^X quoting
win: Subroutine ... redefined warnings on windows for Carp and File::Basename

prevent them from being deleted from %INC as they are reloaded too often
win: results of module tests. not yet release ready
C: postpone init2 after dl_init, GvCV_set of XS init init2