make sure we include features.h to get the hidden define

libc/sysdeps/linux/x86_64/__syscall_error.c

@@ -18,6 +18,7 @@
    02111-1307 USA.  */
 
 #include <errno.h>
+#include <features.h>
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */