archivers/zpaq: fix build on armv6/armv7

The ARM EABI has an unsigned char type. Fix the build
by using explicitly signed chars in the relevant place.

PR:		263389
(cherry picked from commit 6a9ffb1def)

archivers/paq/files/patch-libzpaq.cpp

@@ -0,0 +1,20 @@
+--- libzpaq.cpp.orig	2022-04-18 09:32:11 UTC
++++ libzpaq.cpp
+@@ -2745,7 +2745,7 @@ void Compressor::writeTag() {
+ void Compressor::startBlock(int level) {
+ 
+   // Model 1 - min.cfg
+-  static const char models[]={
++  static const signed char models[]={
+   26,0,1,2,0,0,2,3,16,8,19,0,0,96,4,28,
+   59,10,59,112,25,10,59,10,59,112,56,0,
+ 
+@@ -2774,7 +2774,7 @@ void Compressor::startBlock(int level) {
+   0,0}; // 0,0 = end of list
+ 
+   if (level<1) error("compression level must be at least 1");
+-  const char* p=models;
++  const char* p=(const char*)models;
+   int i;
+   for (i=1; i<level && toU16(p); ++i)
+     p+=toU16(p)+2;