[llvm] [test] Skip some tests on Windows only (PR #95205)

[Eli Friedman via llvm-commits]

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@@ -1,5 +1,5 @@
-FIXME: See if we can fix this in lit by using Unicode strings.
-REQUIRES: shell
+Windows echo does not have good Unicode support.
+UNSUPPORTED: system-windows
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efriedma-quic wrote:

Does something like `RUN: python3 -c 'print("ようこそ")' | FileCheck %s` work?

https://github.com/llvm/llvm-project/pull/95205