Fix the .y file to be robust for newer versions of bison.
Fix the .y file to be robust for newer versions of bison.

h3rb/openshadinglanguage,tectronics/openshadinglanguage,tectronics/openshadinglanguage,qdtk/openshadinglanguage,h3rb/openshadinglanguage,qdtk/openshadinglanguage,code-google-com/openshadinglanguage,h3rb/openshadinglanguage,tectronics/openshadinglanguage,code-google-com/openshadinglanguage,tectronics/openshadinglanguage,code-google-com/openshadinglanguage,qdtk/openshadinglanguage,qdtk/openshadinglanguage,h3rb/openshadinglanguage,code-google-com/openshadinglanguage