[clang] [clang] Don't issue permission error during header search (PR #194015)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

> It can include "the" header because it's found on a later path, right?

You're proposing we go with basically the current patch, which ignores permission errors for both `#include` and `__has_include`?  But also issue a warning for each file we ignore this way?

I guess that's okay; the behavior is self-consistent, and the user will still see the important diagnostic.  (We'd probably want to mark the warning so it isn't suppressed if it's in a system headers.)

I'm not sure it's really an improvement, though; the compilation will almost certainly fail, and the later diagnostics will be pretty useless.

https://github.com/llvm/llvm-project/pull/194015