support tile builtins

[g4titanx]

this pr fixes #563

[antoyo]

Please also enable the tile tests by adressing this comment.

[g4titanx]

@antoyo i need some clarity on impl. the tile intrinsics. currently, I see a few possible approaches:

1. Using get_target_builtin_function, but this fails with "Cannot find target builtin" errors since these don't have GCC builtin equivalents.

2. Creating custom functions with inline assembly, something like:

"llvm.x86.ldtilecfg" => {
    let name = "__rustc_tile_ldtilecfg";
    let func = cx.context.new_function(
        None,
        FunctionType::Internal,
        cx.type_void(),
        &[/* params */],
        name,
        false,
    );
}

[antoyo]

Yeah, get_target_builtin_function won't work.

Perhaps your solution #2 would be the simplest (if that works). You could add the attribute AlwaysInline to make sure it's efficient.

Otherwise, I see another solution involving changing the type Function to an enum that would either take a Function or inline asm, but that might be a lot of work, so I would go with #2 if that works.