[clang] [Clang] Add 'CLANG_ALLOW_IMPLICIT_RPATH' to enable toolchain use of -rpath (PR #82004)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> > I believe right now the `rtlib-rpath` points to the path `${CLANG_BINARY}../lib/${HOST_TRIPLE}/`. I think it's definitely reasonable to not put this on system libraries if that's a solution, since we can generally assume it's a global installation and already covered by the user's library path. Does the Fedora policy only disallow `rpath` on system installs then?
> 
> Right, any official Fedora binaries we build can't have rpath in them, but users can still use rpath in their own applications if they want.

I'd be okay with that solution. The majority of the issues come from people on cluster machines with several conflicting versions of the libraries. The only question is how to determine what a system library is. We could possible just hardcode a few paths depending on the host triple's operating system.

https://github.com/llvm/llvm-project/pull/82004