[llvm] [CMake] Fix building on Haiku and Solaris after c0d5d36dda04cdd409aabc015da0beb810842fcd (PR #78084)

[Rainer Orth via llvm-commits]

rorth wrote:

> Haiku and Solaris need some additional libraries after the commit [c0d5d36](https://github.com/llvm/llvm-project/commit/c0d5d36dda04cdd409aabc015da0beb810842fcd)
> 
> Otherwise fails to link a whole bunch of the tools and other binaries with undefined symbols with accept() and connect().

That's not true on Solaris 11.4, the only Solaris version supported in LLVM.  After 11.3, `libsocket` and `libnsl` have been folded into `libc`.  While those two have been left in place as filters on `libc` for compatibility's sake, it's better not to link unnecessary libraries.

https://github.com/llvm/llvm-project/pull/78084