[compiler-rt] [builtins][CMake] Replace custom target for lse_builtin symlinks (PR #66936)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

Thanks for this, I've also been annoyed by these being remade all the time. I don't really know the details about the cmake constructs at work here though, so I'll defer the review to @smeenai.

https://github.com/llvm/llvm-project/pull/66936