maint: Store released ChangeLog entries in git.

* Makefile.am (EXTRA_DIST): Add ChangeLog.2
(gen-ChangeLog): Only include unreleased entries.
(ChangeLog.2): New rule to re-generate file.

Makefile.am

@@ -18,7 +18,8 @@
 
 ACLOCAL_AMFLAGS = -I am -I m4
 
-EXTRA_DIST = paths ChangeLog.0 ChangeLog.1 summary.sh.in CHECKLIST
+EXTRA_DIST = ChangeLog.0 ChangeLog.1 ChangeLog.2
+EXTRA_DIST += paths summary.sh.in CHECKLIST
 
 EXTRA_DIST += bootstrap bootstrap.conf bootstrap-funclib.sh
 
@@ -40,14 +41,34 @@ dist-hook: gen-ChangeLog
 
 .PHONY: gen-ChangeLog
 gen-ChangeLog:
-	$(AM_V_GEN)if test -d .git; then				\
-		$(top_srcdir)/build-aux/gitlog-to-changelog		\
-			-- v2.0~.. > $(distdir)/cl-t &&			\
-		{ rm -f $(distdir)/ChangeLog &&				\
-		  mv $(distdir)/cl-t $(distdir)/ChangeLog; }		\
+	$(AM_V_GEN)if test -e $(srcdir)/.git; then			\
+	  LC_ALL=en_US.UTF-8 TZ=UTC0					\
+	    $(top_srcdir)/build-aux/gitlog-to-changelog			\
+	      --srcdir=$(srcdir) --					\
+	      v$(PREV_VERSION)~.. > $(distdir)/cl-t &&			\
+	    { printf '\nSee ChangeLog.? for older entries\n'		\
+	      >> $(distdir)/cl-t &&					\
+	      rm -f $(distdir)/ChangeLog &&				\
+	      mv $(distdir)/cl-t $(distdir)/ChangeLog; }		\
 	fi
 
-# dist
+CL2START = f70b506e3746bce45d1b684d5ac5ef513af73df4
+CL2STR = '\n    Copyright (C) 2021-2025 Free Software Foundation, Inc.\n'
+$(srcdir)/ChangeLog.2:
+	$(AM_V_GEN)if test -e $(srcdir)/.git; then			\
+	  LC_ALL=en_US.UTF-8 TZ=UTC0					\
+	    $(top_srcdir)/build-aux/gitlog-to-changelog			\
+	      --srcdir=$(srcdir) --					\
+	      $(CL2START)..v$(PREV_VERSION) > cl-t &&			\
+	    { printf $(CL2STR) >> cl-t &&				\
+	      tail -15 ChangeLog.1 >> cl-t &&				\
+	      if cmp cl-t ChangeLog.2 >/dev/null 2>&1; then		\
+		rm -f cl-t;						\
+	      else							\
+		rm -f $(srcdir)/ChangeLog.2;				\
+		mv -f cl-t $(srcdir)/ChangeLog.2;			\
+	      fi; }							\
+	fi
 
 dist-hook: mtime-NEWS-to-git-HEAD