title: sonarqube included header unkown sources
body: <p>I have a C++ application that includes foo.h which is provided by a 3rd party tool. foo.h includes bar.h, which I do not have. Is there a way to suppress "cannot find the sources for '# include "bar.h'"?</p>
  
  <pre><code>sonar.projectName=MyyAp
  sonar.projectBaseDir=src
  sonar.sources=.
  sonar.cxx.includeDirectories=foo.h,src/includes
  </code></pre>
  
  <p>SonarQube 6.7.1<br>
  Sonar-Scanner 3.0.3.778</p>