strv: make iterator in STRV_FOREACH() declaread in the loop

This also avoids multiple evaluations in STRV_FOREACH_BACKWARDS()

src/sysctl/sysctl.c

@@ -51,8 +51,6 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(Option*, option_free);
 DEFINE_HASH_OPS_WITH_VALUE_DESTRUCTOR(option_hash_ops, char, string_hash_func, string_compare_func, Option, option_free);
 
 static bool test_prefix(const char *p) {
-        char **i;
-
         if (strv_isempty(arg_prefixes))
                 return true;
 
@@ -131,7 +129,6 @@ static int apply_all(OrderedHashmap *sysctl_options) {
                 if (string_is_glob(option->key)) {
                         _cleanup_strv_free_ char **paths = NULL;
                         _cleanup_free_ char *pattern = NULL;
-                        char **s;
 
                         pattern = path_join("/proc/sys", option->key);
                         if (!pattern)
@@ -403,7 +400,6 @@ static int run(int argc, char *argv[]) {
                 }
         } else {
                 _cleanup_strv_free_ char **files = NULL;
-                char **f;
 
                 r = conf_files_list_strv(&files, ".conf", NULL, 0, (const char**) CONF_PATHS_STRV("sysctl.d"));
                 if (r < 0)