Turn -fsemantic-interposition to optimization flag

Turn -fsemantic-interposition to optimization flag

Turn flag_semantic_interposition to optimization option so it can be enabled
with per-function granuality.  This is done by adding the flag among visibility
flags into the symbol table.

gcc/ChangeLog:

2021-11-18  Jan Hubicka  <hubicka@ucw.cz>

	* cgraph.c (cgraph_node::get_availability): Update call of
	decl_replaceable_p.
	(cgraph_node::verify_node): Verify that semantic_interposition flag
	is set correclty.
	* cgraph.h: (symtab_node): Add semantic_interposition flag.
	* cgraphclones.c (set_new_clone_decl_and_node_flags): Clear
	semantic_interposition flag.
	* cgraphunit.c (cgraph_node::finalize_function): Set
	semantic_interposition flag.
	(cgraph_node::add_new_function): Likewise.
	(varpool_node::finalize_decl): Likewise.
	(cgraph_node::create_wrapper): Likewise.
	* common.opt (fsemantic-interposition): Turn to optimization node.
	* lto-cgraph.c (lto_output_node): Stream semantic_interposition.
	(lto_output_varpool_node): Likewise.
	(input_overwrite_node): Likewise.
	(input_varpool_node): Likewise.
	* symtab.c (symtab_node::dump_base): Dump new flag.
	* varasm.c (decl_replaceable_p): Add semantic_interposition_p
	parameter.
	* varasm.h (decl_replaceable_p): Update declaration.
	* varpool.c (varpool_node::ctor_useable_for_folding_p):
	Use semantic_interposition flag.
	(varpool_node::get_availability): Likewise.
	(varpool_node::create_alias): Copy semantic_interposition flag.

gcc/cp/ChangeLog:

2021-11-18  Jan Hubicka  <hubicka@ucw.cz>

	* decl.c (finish_function): Update use of decl_replaceable_p.

gcc/lto/ChangeLog:

2021-11-18  Jan Hubicka  <hubicka@ucw.cz>

	* lto-partition.c (promote_symbol): Clear semantic_interposition flag.

gcc/testsuite/ChangeLog:

2021-11-18  Jan Hubicka  <hubicka@ucw.cz>

	* gcc.dg/lto/semantic-interposition-1_0.c: New test.
	* gcc.dg/lto/semantic-interposition-1_1.c: New test.