build-sys: add headers to EXTRA_DIST to fix 'make distcheck'

Vala autotools, it's all your fault!

Makefile.am

@@ -569,8 +569,68 @@ libsystemd_core_la_LIBADD = \
 # list the .h files as dependencies if we want make dist to work.
 
 EXTRA_DIST += \
-	${libsystemd_basic_la_SOURCES:.c=.h} \
-	${libsystemd_core_la_SOURCES:.c=.h} \
+	src/util.h \
+	src/virt.h \
+	src/label.h \
+	src/hashmap.h \
+	src/set.h \
+	src/strv.h \
+	src/conf-parser.h \
+	src/socket-util.h \
+	src/log.h \
+	src/ratelimit.h \
+	src/exit-status.h \
+	src/unit.h \
+	src/job.h \
+	src/manager.h \
+	src/path-lookup.h \
+	src/load-fragment.h \
+	src/service.h \
+	src/automount.h \
+	src/mount.h \
+	src/swap.h \
+	src/device.h \
+	src/target.h \
+	src/snapshot.h \
+	src/socket.h \
+	src/timer.h \
+	src/path.h \
+	src/load-dropin.h \
+	src/execute.h \
+	src/utmp-wtmp.h \
+	src/dbus.h \
+	src/dbus-manager.h \
+	src/dbus-unit.h \
+	src/dbus-job.h \
+	src/dbus-service.h \
+	src/dbus-socket.h \
+	src/dbus-timer.h \
+	src/dbus-target.h \
+	src/dbus-mount.h \
+	src/dbus-automount.h \
+	src/dbus-swap.h \
+	src/dbus-snapshot.h \
+	src/dbus-device.h \
+	src/dbus-execute.h \
+	src/dbus-path.h \
+	src/cgroup.h \
+	src/mount-setup.h \
+	src/hostname-setup.h \
+	src/selinux-setup.h \
+	src/loopback-setup.h \
+	src/kmod-setup.h \
+	src/locale-setup.h \
+	src/machine-id-setup.h \
+	src/specifier.h \
+	src/unit-name.h \
+	src/fdset.h \
+	src/namespace.h \
+	src/tcpwrap.h \
+	src/cgroup-util.h \
+	src/condition.h \
+	src/dbus-common.h \
+	src/install.h \
+	src/cgroup-attr.h \
 	src/macro.h \
 	src/def.h \
 	src/ioprio.h \