Make PL_hintgv refcounted

Otherwise one can free it (by deleting the *^H glob) and
cause a crash:

$ perl -e 'delete $::{"\cH"}; ${^OPEN}=foo'
Segmentation fault: 11

That happens because PL_hintgv points to a freed scalar, and
GvHV(PL_hintgv) ends up trying to access nonexistent fields.

1 files changed, 1 insertions, 0 deletions

diff --git a/perl.c b/perl.c
index 355d4dd1a5..1361f58277 100644
--- a/perl.c
+++ b/perl.c
@@ -3715,6 +3715,7 @@ S_init_main_stash(pTHX)
     SvREFCNT_inc_simple_void(PL_incgv); /* Don't allow it to be freed */
     GvMULTI_on(PL_incgv);
     PL_hintgv = gv_fetchpvs("\010", GV_ADD|GV_NOTQUAL, SVt_PV); /* ^H */
+    SvREFCNT_inc_simple_void(PL_hintgv);
     GvMULTI_on(PL_hintgv);
     PL_defgv = gv_fetchpvs("_", GV_ADD|GV_NOTQUAL, SVt_PVAV);
     SvREFCNT_inc_simple_void(PL_defgv);