title: Migrate am2cmake
body: <p>I try to transfer into some CMake program and there is a function generating header files from the xml.</p>
  
  <p>Makefile.am</p>
  
  <pre><code>adaptor_glue.hpp: dbus_introspect.xml
      $(DBUSXX_XML2CPP) '$&lt;' --adaptor='$@'
  
  proxy_glue.hpp: dbus_introspect.xml
      $(DBUSXX_XML2CPP) '$&lt;' --proxy='$@'
  </code></pre>
  
  <p>configure</p>
  
  <pre><code>DBUSXX_XML2CPP='$(top_builddir)/dbus-c++/tools/dbusxx-xml2cpp'
  </code></pre>
  
  <p>How I can do it on cmake?</p>