patch 8.1.1567: localtime_r() does not respond to $TZ changes

Problem:    Localtime_r() does not respond to $TZ changes.
Solution:   If $TZ changes then call tzset(). (Tom Ryder)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 66612e8..5c9400e 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -13188,9 +13188,7 @@
 f_strftime(typval_T *argvars, typval_T *rettv)
 {
     char_u	result_buf[256];
-# ifdef HAVE_LOCALTIME_R
     struct tm	tmval;
-# endif
     struct tm	*curtime;
     time_t	seconds;
     char_u	*p;
@@ -13202,11 +13200,7 @@
 	seconds = time(NULL);
     else
 	seconds = (time_t)tv_get_number(&argvars[1]);
-# ifdef HAVE_LOCALTIME_R
-    curtime = localtime_r(&seconds, &tmval);
-# else
-    curtime = localtime(&seconds);
-# endif
+    curtime = vim_localtime(&seconds, &tmval);
     /* MSVC returns NULL for an invalid value of seconds. */
     if (curtime == NULL)
 	rettv->vval.v_string = vim_strsave((char_u *)_("(Invalid)"));