[clang] [Multilib] Extend support for -fmultilib-flag to all targets (PR #182220)

[via cfe-commits]

pzhengqc wrote:

> I don't have any objections to the change. There isn't any reason that the -fmultilib-flag be restricted to Arm and AArch64. As mentioned in the specific comment, I think we should update the title and description to be all targets, with the current implementation.
> 
> I would like someone from the RISCV community to approve in case there is a reluctance to support the flag for RISCV.

Thanks for the feedback, @smithp35. I've updated the description accordingly and also added RISC-V reviewers.

https://github.com/llvm/llvm-project/pull/182220