remove remnants of futex check as it's not necessary anymore.

configure

@@ -3769,7 +3769,7 @@ fi
 done
 
 
-for ac_header in poll.h winsock2.h linux/futex.h sys/epoll.h sys/select.h
+for ac_header in poll.h winsock2.h sys/epoll.h sys/select.h
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
 ac_fn_c_check_header_mongrel "$LINENO" "$ac_header" "$as_ac_Header" "$ac_includes_default"

configure.ac

@@ -24,7 +24,7 @@ AS_IF([test "x$GCC" = "xyes"], [
    CFLAGS="$CFLAGS $MORECFLAGS"
 ])
 
-AC_CHECK_HEADERS([poll.h winsock2.h linux/futex.h sys/epoll.h sys/select.h])
+AC_CHECK_HEADERS([poll.h winsock2.h sys/epoll.h sys/select.h])
 AC_CHECK_FUNCS([fcntl kqueue mmap select dispatch_block port_create])
 
 AC_PATH_PROG(AR, ar)

src/libmowgli/platform/autoconf.h.in

@@ -12,9 +12,6 @@
 /* Define to 1 if you have the `kqueue' function. */
 #undef HAVE_KQUEUE
 
-/* Define to 1 if you have the <linux/futex.h> header file. */
-#undef HAVE_LINUX_FUTEX_H
-
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H