docs: def compiler_preprocessor_verbose(compiler, extraflags):
      """Capture the compiler preprocessor stage in verbose mode
      """
      lines = []
      with open(os.devnull, 'r') as devnull:
          cmd = [compiler, '-E'] 
          cmd += extraflags
          cmd += ['-', '-v']
          p = Popen(cmd, stdin=devnull, stdout=PIPE, stderr=PIPE)
          p.wait()
          p.stdout.close()
          lines = p.stderr.read()
          lines = lines.decode('utf-8')
          lines = lines.splitlines()
      return lines