commit 3f1ddda424353f0f926dd28efa47b0ac61556ce8
Author: Eddie Kohler <ekohler@gmail.com>
Date:   Wed Aug 16 12:37:34 2017 -0400

    Check for memmem declaration; sometimes it is not declared by default.

diff --git a/configure.ac b/configure.ac
index 5b4e3ff..b4dc4fb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -19,6 +19,7 @@ dnl strerror()?
 dnl
 
 AC_REPLACE_FUNCS([strerror memmem])
+AC_CHECK_DECLS([memmem])
 
 
 dnl
@@ -88,7 +89,7 @@ char* strerror(int errno);
 #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