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

[Jay Foad via llvm-commits]

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@@ -1,4 +1,6 @@
-# REQUIRES: shell
+# This test uses symlinks.
+UNSUPPORTED: system-windows
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jayfoad wrote:

No, since this file is _only_ fed into FileCheck, no `#` is needed either for the comments or for the FileCheck directives. I just copied the style used below.

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