[llvm] [BOLT] Enable standalone build (PR #97130)

[Rafael Auler via llvm-commits]

rafaelauler wrote:

> > The reality is that BOLT has been working for a while with the assumption that the libs are in the lib folder even when not installed (just built).
> 
> I've restored that functionality now.

I've tested it and it didn't work for some reason:

```
$ ninja bolt
$ ls lib/libbolt_rt_hugify.a
ls: cannot access 'lib/libbolt_rt_hugify.a': No such file or directory
```

https://github.com/llvm/llvm-project/pull/97130