[clang] [Clang][Driver] Revise Cygwin ToolChain to call linker directly (PR #147960)

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jeremyd2019 wrote:

Thanks!  This was on my mental TODO list but I haven't gotten back to looking at it.  When I was thinking about this, I was thinking about modifying the MinGW linker with a couple of virtual functions and deriving from it for a Cygwin linker, to avoid so much code duplication.  Maybe @mstorsjo can provide an opinion here?

Also, the cygwin.cpp test was based on hurd.cpp, I'm thinking more of those tests are relevant now.

https://github.com/llvm/llvm-project/pull/147960