zlib: fixed to build at native stages to only append 'rc' to $AR at cross stage

Note:

'AR=ar rc' is hardcoded in the Makefile but while cross-compiling we
override it by passing "AR=$arch_target-ar" as makeopt

zlib: fixed comment (SQUASH!)

archiver/zlib/zlib.conf

@@ -29,7 +29,11 @@ if [ "$SDECFG_STATIC" = "0" ] ; then
 	hook_add postmake 3 "zlib_pm"
 fi
 
+# 'AR=ar rc' is hardcoded in the Makefile but while cross-compiling we
+# override it by passing "AR=$arch_target-ar" as makeopt
+if atstage cross; then
 	var_append AR " " "rc"
+fi
 
 var_append makeinstopt " " "prefix=/$prefix"
 var_append makeinstopt " " "mandir=$mandir"