build: generate ChangeLog from git during dist

Makefile.am

@@ -19,6 +19,19 @@ SUBDIRS = \
 	docs \
 	$(NULL)
 
+ChangeLog:
+	$(AM_V_GEN) if test -d "$(srcdir)/.git"; then \
+	  (GIT_DIR=$(top_srcdir)/.git $(top_srcdir)/missing --run git log --stat) | fmt --split-only > $@.tmp \
+	  && mv -f $@.tmp $@ \
+	  || ($(RM) $@.tmp; \
+	      echo Failed to generate ChangeLog, your ChangeLog may be outdated >&2; \
+	      (test -f $@ || echo git-log is required to generate this file >> $@)); \
+	else \
+	  test -f $@ || \
+	  (echo A git checkout and git-log is required to generate ChangeLog >&2 && \
+	  echo A git checkout and git-log is required to generate this file >> $@); \
+	fi
+
 AM_DISTCHECK_CONFIGURE_FLAGS = \
 	--with-udev-base-dir="$$dc_install_base" \
 	--with-systemdsystemunitdir="$$dc_install_base/$(SYSTEMD_UNIT_DIR)" \