[clang] [Clang][Driver] Skip empty strings in getAArch64MultilibFlags (PR #97827)

[Simon Tatham via cfe-commits]

statham-arm wrote:

@asmok-g , I'm confused. This commit doesn't have anything to do with the processing of `-W` options on the clang command line.

Are you sure you've commented on the right PR? If you have, can you provide a full example command line? What was the behaviour before, and what is it afterwards? Why do you say that _this_ commit has caused the change?

https://github.com/llvm/llvm-project/pull/97827