Don't use printf %n.
https://git.savannah.gnu.org/cgit/gnulib.git/commit/lib/vasnprintf.c?id=b954346c6101860c7b462d1b286641d1307afd6c

Index: lib/vasnprintf.c
--- lib/vasnprintf.c.orig
+++ lib/vasnprintf.c
@@ -4858,7 +4858,7 @@ VASNPRINTF (DCHAR_T *resultbuf, size_t *lengthp,
 #endif
                   *fbp = dp->conversion;
 #if USE_SNPRINTF
-# if !(((__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3)) && !defined __UCLIBC__) || ((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__))
+# if 0
                 fbp[1] = '%';
                 fbp[2] = 'n';
                 fbp[3] = '\0';