Allow passing an XML file
Adds command-line option -x to supply a castxml generated XML file to use instead of generating it with pygccxml.
Also adds XML_INPUT option to CMake function autopybind11_add_module to supply this XML file.
Adds command-line option -x to supply a castxml generated XML file to use instead of generating it with pygccxml.
Also adds XML_INPUT option to CMake function autopybind11_add_module to supply this XML file.