re PR c++/70018 (Possible issue around IPO and C++ comdats discovered as pure/const)

re PR c++/70018 (Possible issue around IPO and C++ comdats discovered as pure/const)

	PR ipa/70018
	* cgraph.h (cgraph_node::set_const_flag,
	cgraph_node::set_pure_flag): Update prototype to return bool;
	update comment.
	* cgraph.c (cgraph_node::call_for_symbol_thunks_and_aliases): Thunks
	of interposable symbol are interposable, too.
	(cgraph_set_const_flag_1): Rename to ...
	(set_const_flag_1): ... this one; change to self recursive function
	instead of call_for_symbol_thunks_and_aliases. Handle correctly
	clearnig the flag in all variants and also virtual thunks of const
	functions are pure; track if any change was done.
	(cgraph_node::set_const_flag): Update.
	(struct set_pure_flag_info): New struct.
	(cgraph_set_pure_flag_1): Rename to ...
	(set_pure_flag_1): ... this one; take set_pure_flag_info parameter
	rather than pointer encoded flags; track if any changes was done;
	handle correctly clearning flag and setting flag of aliases already
	declared const.
	(cgraph_node::set_pure_flag): Update.
	(cgraph_node::set_nothrow_flag): Handle correctly clearning the flag.

From-SVN: r235081