Extract minimum PV buffer/AV element size to common definitions

In a nutshell, for a long time the minimum PV length (hardcoded
in Perl_sv_grow) has been 10 bytes and the minimum AV array size
(hardcoded in av_extend_guts) has been 4 elements.

These numbers have been used elsewhere for consistency (e.g.
Perl_sv_grow_fresh) in the past couple of development cycles.
Having a standard definition, rather than hardcoding in multiple
places, is more maintainable. This commit therefore introduces
into perl.h:

    PERL_ARRAY_NEW_MIN_KEY
    PERL_STRLEN_NEW_MIN

(Note: Subsequent commit(s) will actually change the values.)

1 files changed, 2 insertions, 1 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 30a5b35fe2..491cffc305 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -5152,7 +5152,8 @@ Perl_clear_defarray(pTHX_ AV* av, bool abandon)
     else {
         const SSize_t size = AvFILLp(av) + 1;
         /* The ternary gives consistency with av_extend() */
-        AV *newav = newAV_alloc_x(size < 4 ? 4 : size);
+        AV *newav = newAV_alloc_x(size < PERL_ARRAY_NEW_MIN_KEY ?
+                                         PERL_ARRAY_NEW_MIN_KEY : size);
         AvREIFY_only(newav);
         PAD_SVl(0) = MUTABLE_SV(newav);
         SvREFCNT_dec_NN(av);