[libclc] [libclc] Fix commands in compile_to_bc are executed sequentially (PR #130755)

[Fraser Cormack via cfe-commits]

frasercrmck wrote:

Am I right in thinking that CMake 3.27's `DEPENDS_EXPLICIT_ONLY` would also fix this? If so it might be worth documenting this explicitly, both in the PR/commit and in the code? We might be able to refactor this in the future, when LLVM updates its minimum version to 3.27.

https://github.com/llvm/llvm-project/pull/130755