Check for strnlen and provide it if it is not found.

src/Makefile.am

@@ -251,6 +251,7 @@ libbitcoin_common_a_SOURCES = \
 # backward-compatibility objects and their sanity checks are linked.
 libbitcoin_util_a_CPPFLAGS = $(BITCOIN_INCLUDES)
 libbitcoin_util_a_SOURCES = \
+  compat/strnlen.cpp \
   compat/glibc_sanity.cpp \
   compat/glibcxx_sanity.cpp \
   chainparamsbase.cpp \

src/compat.h

@@ -84,4 +84,8 @@ typedef u_int SOCKET;
 #define THREAD_PRIORITY_ABOVE_NORMAL    (-2)
 #endif
 
+#if HAVE_DECL_STRNLEN == 0
+size_t strnlen( const char *start, size_t max_len);
+#endif // HAVE_DECL_STRNLEN
+
 #endif // BITCOIN_COMPAT_H

src/compat/strnlen.cpp

@@ -0,0 +1,18 @@
+// Copyright (c) 2009-2014 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#if defined(HAVE_CONFIG_H)
+#include "config/bitcoin-config.h"
+#endif
+
+#include <cstring>
+
+#if HAVE_DECL_STRNLEN == 0
+size_t strnlen( const char *start, size_t max_len)
+{
+    const char *end = (const char *)memchr(start, '\0', max_len);
+
+    return end ? (size_t)(end - start) : max_len;
+}
+#endif // HAVE_DECL_STRNLEN