https://github.com/kohler/t1utils/issues/8
https://github.com/kohler/t1utils/commit/3f1ddda424353f0f926dd28efa47b0ac61556ce8

--- configure.ac.orig	2017-08-16 18:27:16.000000000 +0200
+++ configure.ac	2017-09-14 09:09:17.077248094 +0200
@@ -19,6 +19,7 @@
 dnl
 
 AC_REPLACE_FUNCS([strerror memmem])
+AC_CHECK_DECLS([memmem])
 
 
 dnl
@@ -88,7 +89,7 @@
 #endif
 
 /* Prototype memmem if we don't have it. */
-#if !HAVE_MEMMEM
+#if !HAVE_MEMMEM || !HAVE_DECL_MEMMEM
 void* memmem(const void* haystack, size_t haystack_len,
              const void* needle, size_t needle_len);
 #endif