Move check_global_declaration from toplev.c to cgraphunit.c

Move check_global_declaration from toplev.c to cgraphunit.c

Unfortunately, toplev.c is a kitchen sink of things that do not belong anywhere
in particular. For example, check_global_declarations is only used in
cgraphunit.c. Moving it there allows us to make it static and remove one call
to symtab_node::get.

gcc/ChangeLog:

2015-09-16  Manuel López-Ibáñez  <manu@gcc.gnu.org>

	* toplev.h (check_global_declaration): Remove declaration.
	* toplev.c (check_global_declaration): Move to ...
	* cgraphunit.c: ... here. Make it static and pass a symtab_node *.
	(analyze_functions): Update call.

From-SVN: r227835