[clang] [Clang] [Driver] add a Cygwin ToolChain (PR #135691)

[Fangrui Song via cfe-commits]

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@@ -0,0 +1,109 @@
+//===--- Cygwin.cpp - Cygwin ToolChain Implementations ----------*- C++ -*-===//
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MaskRay wrote:

In new code, can remove the comments per the updated https://llvm.org/docs/CodingStandards.html#file-headers

https://github.com/llvm/llvm-project/pull/135691