Fix build time problem with MingGW hosts, which do not have a strnlen() function.

2014-03-13  Meador Inge  <meadori@codesourcery.com>

	 * configure.in: Add strnlen to AC_CHECK_DECLS.
	 * config.in: Regenerate.
         * configure: Regenerate.
	 * sysdep.h (strnlen): Add prototype.

         * dwarf.c (strnlen): Move prototype ...
	 * sysdep.h (strnlen): ... to here.