FSF Emacs has a variable garbage-collection-messages, nil by
default.
This allows a user to decide whether to see that
"Garbage collecting..." messages repeatedly.
2001-09-13  Tetsuo Tsukamoto <czkmt(a)remus.dti.ne.jp>
	* alloc.c (garbage_collection_messages): New variable from
	FSF Emacs 19.31.
	(vars_of_alloc): Set up Lisp variable.
	(Fgarbage_collect_1): Variable controls whether to display
	messages.
-- 
Tetsuo Tsukamoto