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

Index: gl/vasnprintf.c
--- gl/vasnprintf.c.orig
+++ gl/vasnprintf.c
@@ -5117,11 +5117,7 @@ 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 __APPLE__ && defined __MACH__)                          \
-        || defined __ANDROID__                                              \
-        || (defined _WIN32 && ! defined __CYGWIN__))
+# if 0
                 fbp[1] = '%';
                 fbp[2] = 'n';
                 fbp[3] = '\0';