Prevent error emission on resolver reentry

The resolver was emitting an error when meeting the same symbol twice.
What is important here is the origin of the resolved symbol, we should
emit an error when the name is similar but the symbol isn't be not when
the resolver is simply meeting the exact same symbol.

gcc/rust/ChangeLog:

	* resolve/rust-toplevel-name-resolver-2.0.cc (insert_macros): Add
	constraint over the ast node id.
	(TopLevel::visit): Likewise.

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

gcc/rust/resolve/rust-toplevel-name-resolver-2.0.cc

@@ -91,7 +91,7 @@ insert_macros (std::vector<PROC_MACRO> &macros, NameResolutionContext &ctx)
     {
       auto res = ctx.macros.insert (macro.get_name (), macro.get_node_id ());
 
-      if (!res)
+      if (!res && res.error ().existing != macro.get_node_id ())
 	{
 	  rust_error_at (UNKNOWN_LOCATION, ErrorCode::E0428,
 			 "macro %qs defined multiple times",
@@ -167,7 +167,7 @@ TopLevel::visit (AST::MacroRulesDefinition &macro)
     {
       auto res = ctx.macros.insert_at_root (macro.get_rule_name (),
 					    macro.get_node_id ());
-      if (!res)
+      if (!res && res.error ().existing != macro.get_node_id ())
 	{
 	  // TODO: Factor this
 	  rich_location rich_loc (line_table, macro.get_locus ());