[libclc] [libclc] Fix installation w/ ENABLE_RUNTIME_SUBNORMAL (PR #109926)

[Aaron Puchert via cfe-commits]

https://github.com/aaronpuchert approved this pull request.

That seems sensible to me.

The absolute path also makes sense because target properties could be requested from a different directory, and then a relative path wouldn't work anymore.

https://github.com/llvm/llvm-project/pull/109926