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

[Tomohiro Kashiwada via cfe-commits]

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kikairoya wrote:

Since `OutputFile` isn't used after this block, it can be simplified like this:
```c++
if (StringRef OutputFile = ...; !has_extension(OutputFile))
  CmdArgs.emplace_back(...);
else
  CmdArgs.push_back(OutputFile);
```

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