Drop ACLOCAL_AMFLAGS

Bump minimum automake requirement to 1.13, starting from which
aclocal can scan m4 directories from AC_CONFIG_MACRO_DIR and
AC_CONFIG_MACRO_DIRS macros. Drop thus obsoleted ACLOCAL_AMFLAGS usage.
This prepares us for future versions of automake that drop support
for ACLOCAL_AMFLAGS

See hrm Feature #899258

Signed-off-by: Marko Lindqvist <cazfi74@gmail.com>

INSTALL

@@ -4,7 +4,7 @@ Installing Freeciv:
 
 This file describes how to compile and install Freeciv. Last time we
 made sure this file is up to date was 16-Jul-06.
-Last minor update was 25-Oct-20.
+Last minor update was 23-Nov-20.
 
 There may be a localized version of this file in the ./doc directory,
 named INSTALL.<locale> (e.g., INSTALL.de).
@@ -99,7 +99,7 @@ contains the generated files.
 
    Autoconf is required to create configure from configure.ac.
 
- - GNU automake version 1.11.4 or better
+ - GNU automake version 1.13 or better
 
    Automake is required to create the various Makefile.in from
    Makefile.am.

Makefile.am

@@ -1,6 +1,5 @@
 ## Process this file with automake to produce Makefile.in
 
-ACLOCAL_AMFLAGS = -I m4 -I dependencies/m4
 AM_DIST_FORMATS = gzip xz zip
 
 if CLIENT

autogen.sh

@@ -242,9 +242,9 @@ real_package_name "autoheader" "ftp://ftp.gnu.org/pub/gnu/autoconf/" 2 65 || DIE
 AUTOHEADER=$REALPKGNAME
 
 # automake and aclocal version numbers must be kept in sync
-real_package_name "automake" "ftp://ftp.gnu.org/pub/gnu/automake/" 1 11 4 || DIE=1
+real_package_name "automake" "ftp://ftp.gnu.org/pub/gnu/automake/" 1 13 || DIE=1
 AUTOMAKE=$REALPKGNAME
-real_package_name "aclocal" "ftp://ftp.gnu.org/pub/gnu/automake/" 1 11 4 || DIE=1
+real_package_name "aclocal" "ftp://ftp.gnu.org/pub/gnu/automake/" 1 13 || DIE=1
 ACLOCAL=$REALPKGNAME
 real_package_name "libtoolize" "ftp://ftp.gnu.org/pub/gnu/libtool/" 2 2 ||
 real_package_name "glibtoolize" "ftp://ftp.gnu.org/pub/gnu/libtool/" 2 2 "" "0" || DIE=1

doc/README.packaging

@@ -19,7 +19,7 @@ Updating from 3.0 to 3.1
    or ~/.civclientrc generated by Freeciv version <= 2.1).
 * Gtk2-client has been dropped completely
 * Sdl1.2 Mixer support has been dropped
-* Minimum automake version is now 1.11.4
+* Minimum automake version is now 1.13
 * Libsqlite3 is now hard requirement
 * Sqlite3 based player authentication support is enabled by default
 * Added gtk3x-client. It's a development version of future gtk4-client