title: g++: error: unrecognized command line option '-Wplacement-new'
body: <p>Recently, I am trying to compile a project with a dependency package called "dealii", but I keep getting this error when compiling:</p>
  
  <p>g++: error: unrecognized command line option '-Wplacement-new'</p>
  
  <p>It seems that g++ does not recognize the option -Wplacement-new. Then I looked at the documentation for gcc, it says -Wplacement-new is a legal warning option flag. But when I invoke "gcc -Wplacement-new ./a.c" I still get this kind of error. </p>
  
  <p>My g++, etc are the latest version. Does anyone know how to fix it? Thanks</p>