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

[via llvm-commits]

pca006132 wrote:

@kloczek it is weird that the system tries to link directly in `/usr/lib64`. I think typically it should build in `/home/tkloczko/rpmbuild/BUILD/bolt-18.1.2.src/x86_64-redhat-linux-gnu`, linked, and then copied to `/usr/lib64` *only when you attempt to install it*. What cmake arguments are you using?

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