CppcheckExecutor: use dedicated ErrorLogger for printing error messages XML (#4985)

This starts to untangle the `ErrorLogger` implementation in
`CppcheckExecutor` which handles three different cases and makes things
unnecessarily complicated.

cli/cppcheckexecutor.cpp

@@ -67,8 +67,23 @@
 #include <windows.h>
 #endif
 
-// TODO: do not directly write to stdout
+class XMLErrorMessagesLogger : public ErrorLogger
+{
+    void reportOut(const std::string & outmsg, Color /*c*/ = Color::Reset) override
+    {
+        std::cout << outmsg << std::endl;
+    }
 
+    void reportErr(const ErrorMessage &msg) override
+    {
+        reportOut(msg.toXML());
+    }
+
+    void reportProgress(const std::string & /*filename*/, const char /*stage*/[], const std::size_t /*value*/) override
+    {}
+};
+
+// TODO: do not directly write to stdout
 
 /*static*/ FILE* CppCheckExecutor::mExceptionOutput = stdout;
 
@@ -97,9 +112,9 @@ bool CppCheckExecutor::parseFromArgs(Settings &settings, int argc, const char* c
         }
 
         if (parser.getShowErrorMessages()) {
-            mShowAllErrors = true;
+            XMLErrorMessagesLogger xmlLogger;
             std::cout << ErrorMessage::getXMLHeader(settings.cppcheckCfgProductName);
-            CppCheck::getErrorMessages(*this);
+            CppCheck::getErrorMessages(xmlLogger);
             std::cout << ErrorMessage::getXMLFooter() << std::endl;
         }
 
@@ -409,11 +424,6 @@ void CppCheckExecutor::reportProgress(const std::string &filename, const char st
 
 void CppCheckExecutor::reportErr(const ErrorMessage &msg)
 {
-    if (mShowAllErrors) {
-        reportOut(msg.toXML());
-        return;
-    }
-
     assert(mSettings != nullptr);
 
     // Alert only about unique errors

cli/cppcheckexecutor.h

@@ -180,11 +180,6 @@ private:
      * Error output
      */
     std::ofstream* mErrorOutput{};
-
-    /**
-     * Has --errorlist been given?
-     */
-    bool mShowAllErrors{};
 };
 
 #endif // CPPCHECKEXECUTOR_H