Make sure Android builds are redumped upon changes to shortlisp

* build-aux/makecounter.sh: New script.
* src/Makefile.in (abs_top_builddir): New variable.
(BUILD_COUNTER_OBJ): Define to build-counter.o
if compiling for Android.
(build-counter.c): New target.  Generate this file using
makecounter.sh upon changes to lisp.mk or shortlisp.
(lisp.mk): Make and load relative to abs_top_builddir.
(emacs$(EXEEXT)): Adjust acordingly.
(mostlyclean): Remove build-counter.c.

build-aux/makecounter.sh

@@ -0,0 +1,43 @@
+#!/bin/sh
+# Generate or update a C file containing an increasing counter
+# variable.
+#
+# Copyright (C) 2023 Free Software Foundation, Inc.
+#
+# This file is part of GNU Emacs.  GNU Emacs is free software: you can
+# redistribute it and/or modify it under the terms of the GNU General
+# Public License as published by the Free Software Foundation, either
+# version 3 of the License, or (at your option) any later version.
+#
+# GNU Emacs is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with GNU Emacs.	 If not, see <https://www.gnu.org/licenses/>.
+
+set -e
+
+curcount=
+if test -f "$1"; then
+    curcount=`cat "$1" | grep = | cut -d= -f2 \
+		  | sed -e 's/;//' -e 's/ //'`
+fi
+
+curcount=`expr 1 + $curcount 2>/dev/null || echo 0`
+
+cat > $1 <<EOF
+/* Generated automatically by makecounter.sh.  Do not edit! */
+
+#include <config.h>
+
+#ifdef HAVE_ANDROID
+#define EXPORT __attribute__ ((visibility ("default")))
+#endif /* HAVE_ANDROID */
+
+#ifdef EXPORT
+EXPORT
+#endif /* EXPORT */
+int counter = $curcount;
+EOF