Make const redef warnings default in newXS

There is no reason why constant redefinition warnings should be
default warnings for sub foo(){1}, but not for newCONSTSUB (which
calls newXS, which triggers the warning).

To make this work properly, I also had to import sv.c’s ‘are these
const subs from the same SV originally?’ logic.  Constants created
with XS can have NULL for the SV (they return an empty list or
&PL_sv_undef), which means sv.c’s logic will stop *this=\&that from
warning if both this and that are such XS-created constants.
newCONSTSUB needed to be consistent with that.  It required tweaking a
test I added a few commits ago, which arguably shouldn’t have warned
the way it was written.

As of this commit (and before it, too, come to think of it),
newXS_len_flags’s calling convention is quite awful and would need to
be throughly re-thunk before being made into an API, or probably sim-
ply never made into an API.

1 files changed, 1 insertions, 1 deletions

diff --git a/proto.h b/proto.h
index 8bec0b273b..19f52d58aa 100644
--- a/proto.h
+++ b/proto.h
@@ -2781,7 +2781,7 @@ PERL_CALLCONV CV *	Perl_newXS_flags(pTHX_ const char *name, XSUBADDR_t subaddr,
 #define PERL_ARGS_ASSERT_NEWXS_FLAGS	\
 	assert(subaddr); assert(filename)
 
-PERL_CALLCONV CV *	Perl_newXS_len_flags(pTHX_ const char *name, STRLEN len, XSUBADDR_t subaddr, const char *const filename, const char *const proto, U32 flags)
+PERL_CALLCONV CV *	Perl_newXS_len_flags(pTHX_ const char *name, STRLEN len, XSUBADDR_t subaddr, const char *const filename, const char *const proto, SV **const_svp, U32 flags)
 			__attribute__nonnull__(pTHX_3)
 			__attribute__nonnull__(pTHX_4);
 #define PERL_ARGS_ASSERT_NEWXS_LEN_FLAGS	\