[BUILD] OptiX support on Windows

[AlexeySmolenchuk]

I managed to build OSL project on Windows without OptiX support. With clang+llvm-18.1.8

Once I add OptiX support OptiX 8.0 or OptiX 9.0 CUDA 12.0

[build] C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\VC\Tools\MSVC\14.42.34433\include\yvals_core.h(892): error: static assertion failed with "error STL1002: Unexpected compiler version, expected CUDA 12.4 or newer."

When I update to CUDA 13.0

[build] clang++: warning: CUDA version is newer than the latest supported version 12.3 [-Wunknown-cuda-version]
[build] In file included from <built-in>:1:
[build] C:\Users\Alexey\sandbox\clang+llvm-18.1.8-x86_64-pc-windows-msvc\lib\clang\18\include\__clang_cuda_runtime_wrapper.h:387:10: fatal error: 'texture_fetch_functions.h' file not found
[build]   387 | #include "texture_fetch_functions.h"
[build]       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~
[build] 1 error generated when compiling for sm_60.

Also, dl and rt libraries are hardcoded here, but I'm sure it won't work on Windows. https://github.com/AcademySoftwareFoundation/OpenShadingLanguage/blob/main/src/cmake/externalpackages.cmake#L153