[clang] Extend -Wnonportable-include-path with a warning about trailing whitespace or dots (PR #96960)

[Tobias Mayer via cfe-commits]

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@@ -0,0 +1,11 @@
+// REQUIRES: case-insensitive-filesystem
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tobias-mayer wrote:

I wasn't sure about this but I think I could remove that.
The behavior should be as follows:
- Linux: You get the new warning and a file not found error.
- Windows: You only get the new warning as the file is still found.
- Mac: Warning + error just as on Linux. Case sensitivity shouldn't matter in both cases.

https://github.com/llvm/llvm-project/pull/96960