[clang] Fix preprocessed block comment newline on windows containing extra carriage return (PR #205084)

[Joel E. Denny via cfe-commits]

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@@ -112,6 +112,13 @@
         ),
     )
 )
+
+cr = "\r" if platform.system() == "Darwin" else r"\r"
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jdenny-ornl wrote:

`cr = "\r"` is not portable beyond Darwin?

https://github.com/llvm/llvm-project/pull/205084