WIP: Opencl to SPIR-V ahead-of-time compilation

This does not yet use the pystencils' cache folder or disk caching of the compilation.

This can be used to embed compiled bytecode into waLBerla executables as I do with my Vulkan wrapper. Not sure if this is a good way to go but at least we can experiment with it.

A good way to proceed with this MR is also a comparison between hip/sicl/ocl/vulkan in order to identify a suitable backend for pystencils.

pystencils/opencl/spirv.py

@@ -24,6 +24,13 @@ def _opencl_to_spriv(opencl_code,
 
     clspv (https://github.com/google/clspv) ...takes a while to compile
 
+      --cl-std=<value>
+        =CL1.0
+        =CL1.1
+        =CL1.2
+        =CL2.0
+        =CLC++
+
     For OpenCL SPIRV (loaded by OpenCL runtime):
 
         Tools:
@@ -74,6 +81,7 @@ def _opencl_to_spriv(opencl_code,
                               *OCL_FAST_MATH_FLAGS,
                               *(['-cl-single-precision-constant'] if silence_warnings else []),
                               cl_file,
+                              f'-cl-std=CL{opencl_version}',
                               '-I', get_pystencils_include_path(),
                               '-O3',
                               *(['-w'] if silence_warnings else []),