Issue #13134: optimize finding single-character strings using memchr
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 3a38398..dbaa5c4 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -515,6 +515,9 @@
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H
 
+/* Define to 1 if you have the `memrchr' function. */
+#undef HAVE_MEMRCHR
+
 /* Define to 1 if you have the `mkdirat' function. */
 #undef HAVE_MKDIRAT