build: Add 'EMACS' silent rule.

* Makefile.am (AM_V_EMACS, AM_V_EMACS_, AM_V_EMACS_0): New variables.
* emacs.am [HAVE_EMACS] ($(AUTOLOADS)): Use $(AM_V_EMACS).

Makefile.am

@@ -484,3 +484,7 @@ AM_V_DL_0 = @echo "  DL      " $@;
 AM_V_DOT = $(AM_V_DOT_$(V))
 AM_V_DOT_ = $(AM_V_DOT_$(AM_DEFAULT_VERBOSITY))
 AM_V_DOT_0 = @echo "  DOT     " $@;
+
+AM_V_EMACS = $(AM_V_EMACS_$(V))
+AM_V_EMACS_ = $(AM_V_EMACS_$(AM_DEFAULT_VERBOSITY))
+AM_V_EMACS_0 = @echo "  EMACS   " $@;

emacs.am

 # GNU Guix --- Functional package management for GNU
 # Copyright © 2014, 2015, 2016 Alex Kost <alezost@gmail.com>
+# Copyright © 2016 Mathieu Lirzin <mthl@gnu.org>
 #
 # This file is part of GNU Guix.
 #
@@ -60,7 +61,7 @@ dist_lisp_DATA =				\
 nodist_lisp_DATA = emacs/guix-config.el
 
 $(AUTOLOADS): $(ELFILES)
-	$(EMACS) --batch --eval						\
+	$(AM_V_EMACS)$(EMACS) --batch --eval				\
 	  "(let ((backup-inhibited t)					\
 	         (generated-autoload-file				\
 	          (expand-file-name \"$(AUTOLOADS)\" \"$(srcdir)\")))	\