Add missing declarations to pg_config.h.in

Add missing pg_config.h.in declarations from 09be391126
where the corresponding autoconf/meson declarations were
added.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/70145721-6949-4ABF-BB54-63F866488DF8@yesql.se

src/include/pg_config.h.in

@@ -123,6 +123,10 @@
    */
 #undef HAVE_DECL_STRSEP
 
+/* Define to 1 if you have the declaration of `timingsafe_bcmp', and to 0 if
+   you don't. */
+#undef HAVE_DECL_TIMINGSAFE_BCMP
+
 /* Define to 1 if you have the <editline/history.h> header file. */
 #undef HAVE_EDITLINE_HISTORY_H
 
@@ -455,6 +459,9 @@
 /* Define to 1 if curl_global_init() is guaranteed to be thread-safe. */
 #undef HAVE_THREADSAFE_CURL_GLOBAL_INIT
 
+/* Define to 1 if you have the `timingsafe_bcmp' function. */
+#undef HAVE_TIMINGSAFE_BCMP
+
 /* Define to 1 if your compiler understands `typeof' or something similar. */
 #undef HAVE_TYPEOF