Clang: Add clazy argument to ignore included files

ignore-include-files flag  does not improve performance
currently. But if we decide to use -I for some of our
include paths than this parameter will continue to skip
them for clazy diagnostics.

Change-Id: I8ff02edf224f680f88f1b178098787c0e2a629cb
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/clangcodemodel/clangeditordocumentprocessor.cpp

@@ -579,6 +579,11 @@ static QStringList clazyCommandLine()
     QStringList result;
     addXclangArg(result, "-add-plugin", "clang-lazy");
     addXclangArg(result, "-plugin-arg-clang-lazy", clazyChecks);
+
+    // NOTE: we already use -isystem for all include paths to make libclang skip diagnostics for
+    // all of them. That means that ignore-included-files will not change anything unless we decide
+    // to return the original -I prefix for some include paths.
+    addXclangArg(result, "-plugin-arg-clang-lazy", "ignore-included-files");
     return result;
 }