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

[via cfe-commits]

================
@@ -0,0 +1,11 @@
+// REQUIRES: case-insensitive-filesystem
----------------
zmodem wrote:

Hmm, I think Mac's qualifies as a case-insensitive-filesystem, but I don't think it ignores trailing spaces/dots like Windows does(?).

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