* flags.h (flag_optimize_sibling_calls): Declare.
	* calls.c (expand_call): Fail sibcall when
	!flag_optimize_sibling_calls
	* invoke.texi (flag_optimize_sibling_calls): Document.
	* toplev.c (flag_optimize_sibling_calls): New global variable.
	(f_options): Add flag_optimize_sibling_calls.
	(rest_of_compilation): Conditionize
	optimize_sibling_and_tail_recursive_calls by
	flag_optimize_sibling_calls.
	(main): Set flag_optimize_sibling_calls for -O2.
	* stmt.c (expand_return): Conditionize tail recursion by
	flag_optimize_sibling_calls.

From-SVN: r32802