don't segfault given string repeat count larger than 2^31

E.g., this overflows INT_MAX and overruns heap memory:

    $ perl -le 'print "v"x(2**31+1)'
    [Exit 139 (SEGV)]

(Perl_repeatcpy): Use the same type for "count" as our sole
callers in pp.c: IV (long), not I32 (int).  Otherwise, passing
the wider value to a narrower "I32 count"

embed.fnc

@@ -1066,7 +1066,7 @@ EXp	|SV*|reg_qr_package|NN REGEXP * const rx
 
 : FIXME - why the E?
 Ep	|void	|regprop	|NULLOK const regexp *prog|NN SV* sv|NN const regnode* o
-Anp	|void	|repeatcpy	|NN char* to|NN const char* from|I32 len|I32 count
+Anp	|void	|repeatcpy	|NN char* to|NN const char* from|I32 len|IV count
 AnpP	|char*	|rninstr	|NN const char* big|NN const char* bigend \
 				|NN const char* little|NN const char* lend
 Ap	|Sighandler_t|rsignal	|int i|Sighandler_t t

proto.h

@@ -3244,7 +3244,7 @@ PERL_CALLCONV void	Perl_regprop(pTHX_ const regexp *prog, SV* sv, const regnode*
 #define PERL_ARGS_ASSERT_REGPROP	\
 	assert(sv); assert(o)
 
-PERL_CALLCONV void	Perl_repeatcpy(char* to, const char* from, I32 len, I32 count)
+PERL_CALLCONV void	Perl_repeatcpy(char* to, const char* from, I32 len, IV count)
 			__attribute__nonnull__(1)
 			__attribute__nonnull__(2);
 #define PERL_ARGS_ASSERT_REPEATCPY	\

util.c

@@ -3404,27 +3404,27 @@ Perl_my_pclose(pTHX_ PerlIO *ptr)
 
 #define PERL_REPEATCPY_LINEAR 4
 void
-Perl_repeatcpy(register char *to, register const char *from, I32 len, register I32 count)
+Perl_repeatcpy(register char *to, register const char *from, I32 len, register IV count)
 {
     PERL_ARGS_ASSERT_REPEATCPY;
 
     if (len == 1)
 	memset(to, *from, count);
     else if (count) {
 	register char *p = to;
-	I32 items, linear, half;
+	IV items, linear, half;
 
 	linear = count < PERL_REPEATCPY_LINEAR ? count : PERL_REPEATCPY_LINEAR;
 	for (items = 0; items < linear; ++items) {
 	    register const char *q = from;
-	    I32 todo;
+	    IV todo;
 	    for (todo = len; todo > 0; todo--)
 		*p++ = *q++;
         }
 
 	half = count / 2;
 	while (items <= half) {
-	    I32 size = items * len;
+	    IV size = items * len;
 	    memcpy(p, to, size);
 	    p     += size;
 	    items *= 2;