[clang] [clang][HeaderSearch] Treat permission-denied include paths as non-fatal (PR #177582)

[Aaron Ballman via cfe-commits]

================
@@ -0,0 +1,9 @@
+// Needs chmod
+// UNSUPPORTED: system-windows
----------------
AaronBallman wrote:

Because this can be hit on Windows, I think we should have test coverage there as well if possible.

https://github.com/llvm/llvm-project/pull/177582