gccrs: nr2.0: Improve error handling

gccrs: nr2.0: Improve error handling

gcc/rust/ChangeLog:

	* resolve/rust-early-name-resolver-2.0.cc
	(Early::build_import_mapping): Avoid outputting an "unresolved
	import" error if other errors are outputted during resolution.
	* resolve/rust-early-name-resolver-2.0.h
	(Early::resolve_path_in_all_ns): Collect path resolution errors
	while avoiding duplicate errors for resolutions in each
	namespace.
	* resolve/rust-forever-stack.h
	(ForeverStack::resolve_path): Add parameter for collecting
	errors.
	(ForeverStack::find_starting_point): Likewise.
	(ForeverStack::resolve_segments): Likewise.
	* resolve/rust-forever-stack.hxx
	(check_leading_kw_at_start): Likewise.
	(ForeverStack::find_starting_point): Likewise.
	(ForeverStack::resolve_segments): Likewise.
	(ForeverStack::resolve_path): Likewise.
	* resolve/rust-name-resolution-context.h
	(NameResolutionContext::resolve_path): Add optional parameter
	for collecting errors.

gcc/testsuite/ChangeLog:

	* rust/compile/nr2/exclude: Remove entry.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>