This was discussed on the list some months ago:
http://www.mail-archive.com/lyx-devel@lists.lyx.org/msg179563.html
FileName const configure_script(addName(system_support().absFileName(), "configure.py"));
configure_command_ = os::python() + ' ' +
- quoteName(configure_script.toFilesystemEncoding(), quote_python) +
+ quoteName(configure_script.toFilesystemEncoding()) +
with_version_suffix() + " --binary-dir=" +
quoteName(FileName(binary_dir().absFileName()).toFilesystemEncoding());