build: Bump automake version to 1.11

It was needed for xz distribution tarballs, and allows us to get rid of
the conditional silent-rules support.

README

@@ -43,7 +43,7 @@ To prepare the dpkg source tree from git before starting the build process
 some required software needs to be installed:
 
   GNU autoconf >= 2.60
-  GNU automake >= 1.8
+  GNU automake >= 1.11
   GNU gettext >= 0.18.2 (or just autopoint if using --disable-nls)
   flex
 

configure.ac

@@ -10,10 +10,8 @@ AC_CONFIG_AUX_DIR([build-aux])
 
 AC_USE_SYSTEM_EXTENSIONS
 
-AM_INIT_AUTOMAKE([1.8 foreign nostdinc no-dist-gzip dist-xz])
-
-m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])],
-                            [AC_SUBST([AM_DEFAULT_VERBOSITY], [1])])
+AM_INIT_AUTOMAKE([1.11 foreign nostdinc no-dist-gzip dist-xz])
+AM_SILENT_RULES([yes])
 
 AM_GNU_GETTEXT_VERSION([0.18.2])
 AM_GNU_GETTEXT([external])