gccrs: Loop on expansion if a new export has been defined

gccrs: Loop on expansion if a new export has been defined

When a use statement requires a reexported item it cannot find it in
the same pass, an additional pass shall be performed. This means we need
to detect whether a new item has been reexported and resolve until the
end.

gcc/rust/ChangeLog:

	* resolve/rust-early-name-resolver-2.0.cc (Early::Early): Add dirty
	flag initialization.
	(Early::go): Set dirty flag using top level resolver.
	* resolve/rust-early-name-resolver-2.0.h: Add dirty flag.
	* resolve/rust-toplevel-name-resolver-2.0.cc (TopLevel::TopLevel):
	Initialize dirty flag.
	(TopLevel::insert_or_error_out): Set dirty flag on successful
	namespace modification.
	* resolve/rust-toplevel-name-resolver-2.0.h: Add dirty flag.
	* rust-session-manager.cc (Session::expansion): Modify fixed point
	condition to include name resolution modifications.

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