[clang] [Driver][DragonFly] Fixes for linker path and command-line option handling (PR #69095)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> > This appears to have broken some bots: [lab.llvm.org/buildbot/#/builders/119/builds/15633](https://lab.llvm.org/buildbot/#/builders/119/builds/15633) [lab.llvm.org/buildbot/#/builders/60/builds/14449](https://lab.llvm.org/buildbot/#/builders/60/builds/14449)
> > Can you investigate and get those bots back to green?
> 
> Ping?

fixed by e65721c3a1ee3ee4aa43499882f6d71dc9368daf

I guess this Windows bot is related to the CMake `DEFAULT_SYSROOT` variable that I want to deprecate in https://reviews.llvm.org/D158218

https://github.com/llvm/llvm-project/pull/69095