[llvm] [BOLT] Enable standalone build (PR #87196)

[John Ericson via llvm-commits]

Ericson2314 wrote:

@pca006132 What I think that boils down to is that the remove-only parts (not the `CMAKE_INSTALL_LIBDIR` parts) of https://github.com/NixOS/nixpkgs/blob/bca374aa31d4a9d0446216478a4242d629e72258/pkgs/development/compilers/llvm/17/bolt/gnu-install-dirs.patch should in fact go upstream.

https://github.com/llvm/llvm-project/pull/87196