Fix #118020: Cycles OptiX OSL crashes

Turns out we were not building OSL with OptiX enabled anymore.
Also check now if the OSL builds has OptiX support and if not
disable it in Cycles.

Building OSL with support for this (still) does not require
either the OptiX SDK or CUDA, it only needs LLVM.

Pull Request: https://projects.blender.org/blender/blender/pulls/118234

build_files/build_environment/cmake/osl.cmake

@@ -43,6 +43,10 @@ set(OSL_EXTRA_ARGS
   -DPython_EXECUTABLE=${PYTHON_BINARY}
 )
 
+if(NOT APPLE)
+  list(APPEND OSL_EXTRA_ARGS -DOSL_USE_OPTIX=ON)
+endif()
+
 ExternalProject_Add(external_osl
   URL file://${PACKAGE_DIR}/${OSL_FILE}
   DOWNLOAD_DIR ${DOWNLOAD_DIR}