Added cmake option to enable/disable RTTI.
Added cmake option to enable/disable RTTI.

Anteru/OpenShadingLanguage,Anteru/OpenShadingLanguage,svenstaro/OpenShadingLanguage,mcanthony/OpenShadingLanguage,lgritz/OpenShadingLanguage,yaroslav-tarasov/OpenShadingLanguage,Anteru/OpenShadingLanguage,rlmh/OpenShadingLanguage,imageworks/OpenShadingLanguage,brechtvl/OpenShadingLanguage,lgritz/OpenShadingLanguage,brechtvl/OpenShadingLanguage,mcanthony/OpenShadingLanguage,mcanthony/OpenShadingLanguage,brechtvl/OpenShadingLanguage,svenstaro/OpenShadingLanguage,rlmh/OpenShadingLanguage,aconty/OpenShadingLanguage,lgritz/OpenShadingLanguage,gzorin/OpenShadingLanguage,imageworks/OpenShadingLanguage,gzorin/OpenShadingLanguage,aconty/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,juvenal/OpenShadingLanguage,imageworks/OpenShadingLanguage,lgritz/OpenShadingLanguage,brechtvl/OpenShadingLanguage,rlmh/OpenShadingLanguage,aconty/OpenShadingLanguage,johnhaddon/OpenShadingLanguage,mcanthony/OpenShadingLanguage,johnhaddon/OpenShadingLanguage,brechtvl/OpenShadingLanguage,juvenal/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,lgritz/OpenShadingLanguage,gzorin/OpenShadingLanguage,yaroslav-tarasov/OpenShadingLanguage,juvenal/OpenShadingLanguage,svenstaro/OpenShadingLanguage,sjparker/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,aconty/OpenShadingLanguage,yaroslav-tarasov/OpenShadingLanguage,sjparker/OpenShadingLanguage,imageworks/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,rlmh/OpenShadingLanguage,svenstaro/OpenShadingLanguage,juvenal/OpenShadingLanguage,sjparker/OpenShadingLanguage,gzorin/OpenShadingLanguage,imageworks/OpenShadingLanguage,sjparker/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,johnhaddon/OpenShadingLanguage,aconty/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,yaroslav-tarasov/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,gzorin/OpenShadingLanguage,johnhaddon/OpenShadingLanguage,Anteru/OpenShadingLanguage