gccrs: Add name resolution for on globbing use decl

gccrs: Add name resolution for on globbing use decl

This is the first part of the code required to enable globbing on use
declarations.

gcc/rust/ChangeLog:

	* resolve/rust-toplevel-name-resolver-2.0.cc (GlobbingVisitor::visit):
	Insert names into their namespace.
	(TopLevel::visit): Insert ast module.
	(TopLevel::handle_use_dec): Resolve use declaration.
	(TopLevel::handle_use_glob): Use globbing visitor.
	(flatten_list): Use globbing path vector.
	(flatten_glob): Likewise.
	(flatten): Likewise.
	(prefix_subpaths): Add a function to prefix subpath.
	* resolve/rust-toplevel-name-resolver-2.0.h (class GlobbingVisitor):
	Add globbing visitor.
	* util/rust-hir-map.cc (Mappings::insert_ast_module): Add function to
	insert module in module hashmap.
	(Mappings::lookup_ast_module): Add function to retrieve ast module.
	* util/rust-hir-map.h: Add module map and getter/setter prototypes.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>