`make distcheck` has an expectation that, if only --prefix is
specified, all other potentially-configurable paths are somehow
relative to '${prefix}', e.g. bindir defaults to '${prefix}/bin'.

We get an absolute path from $(pkg-config systemd ...) at all times
in case systemd.pc is present, and an empty path in case it is not,
which collides with the aforementioned expectation two ways. Add an
internal --with-dcprefix configure option for the sake of distcheck.
---
 Makefile.am  | 1 +
 configure.ac | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/Makefile.am b/Makefile.am
index e292d3b9..52a3e6c4 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -23,6 +23,7 @@ libnftables_LIBVERSION = 2:0:1
 ###############################################################################
 
 ACLOCAL_AMFLAGS = -I m4
+AM_DISTCHECK_CONFIGURE_FLAGS = --with-dcprefix='$${prefix}'
 
 EXTRA_DIST =
 BUILT_SOURCES =
diff --git a/configure.ac b/configure.ac
index 626c641b..198b3be8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -122,6 +122,11 @@ AC_ARG_WITH([unitdir],
 		AS_IF([test -z "$unitdir"], [unitdir='${prefix}/lib/systemd/system'])
 	])
 AC_SUBST([unitdir])
+AC_ARG_WITH([dcprefix],
+        [AS_HELP_STRING([Extra path inserted for distcheck])],
+        [dcprefix="$withval"])
+AC_SUBST([dcprefix])
+AS_IF([test -z "$unitdir"], [unitdir='${prefix}/lib/systemd/system'], [unitdir='${dcprefix}'"$unitdir"])
 
 
 AC_CONFIG_FILES([					\
-- 
2.51.0