build: Set minimum Automake version to 1.13

Author: hebasto

configure.ac

@@ -36,14 +36,14 @@ dnl faketime breaks configure and is only needed for make. Disable it here.
 unset FAKETIME
 
 dnl Automake init set-up and checks
-AM_INIT_AUTOMAKE([no-define subdir-objects foreign])
+AM_INIT_AUTOMAKE([1.13 no-define subdir-objects foreign])
 
 dnl faketime messes with timestamps and causes configure to be re-run.
 dnl --disable-maintainer-mode can be used to bypass this.
 AM_MAINTAINER_MODE([enable])
 
 dnl make the compilation flags quiet unless V=1 is used
-m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
+AM_SILENT_RULES([yes])
 
 dnl Compiler checks (here before libtool).
 if test "x${CXXFLAGS+set}" = "xset"; then