[libclc] [libclc] Fix a couple of issues preventing in-tree builds (PR #87505)

[Fraser Cormack via cfe-commits]

frasercrmck wrote:

> ```
>       set( spv_suffix ${arch_suffix}.spv )
>       add_custom_command( OUTPUT "${spv_suffix}"
>         COMMAND ${LLVM_SPIRV} ${spvflags} -o "${spv_suffix}" ${builtins_opt_lib_tgt}
>         DEPENDS ${builtins_link_lib_tgt} )
> ```
> 
> I think that ought to be `DEPENDS ${builtins_opt_lib_tgt}`. Do you need me to send a PR for that?

Hmm yes you might be right. Just to confirm, does that fix the problem for you?

I can't be sure but it seems like that was a problem before 61efea7142e904e6492e1ce0566ec23d9d221c1e when I last touched it, as least from a simple reading of the CMake.

https://github.com/llvm/llvm-project/pull/87505