Come up with constructors of symtab_node, cgraph_node and varpool_node.

Come up with constructors of symtab_node, cgraph_node and varpool_node.

2019-12-09  Martin Liska  <mliska@suse.cz>

	PR ipa/92737
	* cgraph.c (symbol_table_test::symbol_table_test): Fix
	coding style.
	* cgraph.h (symtab_node::symtab_node): New constructor.
	(cgraph_node::cgraph_node): Likewise.
	(varpool_node::varpool_node): Likewise.
	(symbol_table::allocate_cgraph_symbol): Use newly
	created constructor.
	(symbol_table::allocate_cgraph_symbol): Remove.
	* cgraphunit.c (symtab_terminator): Likewise.
	* varpool.c (varpool_node::create_empty): Use newly
	created constructor.

From-SVN: r279109