For Metal project---adding drivers

[gulugulubing]

Start a minimal Metal bindings and mimic cuda or ocl's style. I am not sure whether it's a right direction.
One major blocker was an Objective-C interop RTTI/linker problem in D:

• Storing extern(Objective-C) interface types directly in wrapper structs sometimes(not always, but at most time, strange) caused LDC to emit RTTI/classinfo references such as __Interface / __Class.
• Those symbols are not provided by the Objective-C runtime, which led to undefined-symbol linker errors.
• The fix was to store Objective-C handles as raw void* internally and cast at the wrapper boundary, avoiding unwanted RTTI emission.

[gulugulubing]

@asindarov, is this style of index consistent with your compiler's side progress? And If you are working on how to inline these functions, I found MPM.addPass(llvm::ModuleInlinerWrapperPass()); works https://github.com/gulugulubing/ldc/tree/Metal-OS26-LLVM20.

[asindarov]

yes, it is. I will see if I can run the module level pass during code gen for llvm bitcode

[gulugulubing]

At first, I didn't wanna touch the codes related to cuda and ocl, but I found I had to use a zero-argument template to avoid compiling this file. This is related to #95