With glibc 2.23

emerge-falco libmtp

x86_64-cros-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I.. -I/build/falco/usr/include/libusb-1.0 -O2 -pipe -clang-syntax -O2 -pipe -march=corei7 -g -fno-exceptions -fno-unwind-tables -fno-asynchronous-unwind-tables -clang-syntax -clang-syntax -Wall -Wmissing-prototypes -c util.c  -fPIC -DPIC -o .libs/libmtp_la-util.o
In file included from util.c:38:
./util.h:29:7: error: expected identifier or '('
char *strndup (const char *s, size_t n);
      ^
/usr/include/bits/string2.h:1319:26: note: expanded from macro 'strndup'
#   define strndup(s, n) __strndup (s, n)
                         ^
/usr/include/bits/string2.h:1300:4: note: expanded from macro '__strndup'

The patch below fixes that

--- src/util.hh	2016-06-02 11:38:16.522773205 -0700
+++ src/util.h	2016-06-02 11:37:04.699095234 -0700
@@ -20,6 +20,9 @@
  * Boston, MA 02111-1307, USA.
  */
 
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
 #ifndef __MTP__UTIL__H
 #define __MTP__UTIL__H