dnl Chroot support.
AC_CHECK_FUNCS([chroot unshare])
- AC_CHECK_HEADERS([sched.h sys/param.h sys/mount.h])
+ AC_CHECK_HEADERS([sched.h sys/param.h sys/mount.h tr1/unordered_set])
dnl lutimes and lchown: used when canonicalizing store items.
dnl posix_fallocate: used when extracting archives.