[clang] [LinkerWrapper] Fix `-Xoffload-linker a=b` in offloading (PR #100270)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> I think LLVM generally doesn't follow the convention that `-a x` and `--abc=x`?

`cl::opt` options are arbitrary, but this isn't about convention really, it's for things like `-Xoffload-linker -Wl,-plugin-opt=blah` not being passed correctly.

https://github.com/llvm/llvm-project/pull/100270