issue #3760 C++ using directives are not understood (Origin: bugzilla #617285)

Author: doxygen

src/doxygen.cpp

@@ -2194,7 +2194,7 @@ static void findUsingDeclImports(const Entry *root)
     {
       AUTO_TRACE_ADD("found scope '{}'",scope->name());
       SymbolResolver resolver;
-      const Definition *def = resolver.resolveSymbol(scope,root->name);
+      const Definition *def = resolver.resolveSymbol(root->name.startsWith("::") ? nullptr : scope,root->name);
       if (def && def->definitionType()==Definition::TypeMember)
       {
         int i=root->name.find("::");

src/scanner.l

@@ -1976,7 +1976,7 @@ NONLopt [^\n]*
                                           BEGIN(Using);
                                         }
 <Using>"namespace"{BN}+                 { lineCount(yyscanner); BEGIN(UsingDirective); }
-<Using>({ID}{BN}*("::"|"."){BN}*)*({ID}|{OPERATOR}) {
+<Using>("::")?({ID}{BN}*("::"|"."){BN}*)*({ID}|{OPERATOR}) {
                                           lineCount(yyscanner);
                                           yyextra->current->name=yytext;
                                           yyextra->current->fileName = yyextra->fileName;