gccrs: Fix path expr segment parsing with generic path

gccrs: Fix path expr segment parsing with generic path

When a token was identified as bit left shift it slipped through the
parser and resulted in an error.

gcc/rust/ChangeLog:

	* parse/rust-parse-impl.h (Parser::parse_path_expr_segment): Accept
	left shift tokens in order to let generic parsing function split the
	token.

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