[clang] [clang] Implement -Wmissing-include-dirs (PR #94827)

[Braden Helmer via cfe-commits]

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@@ -809,4 +809,7 @@ def warn_android_unversioned_fallback : Warning<
 
 def err_drv_triple_version_invalid : Error<
   "version '%0' in target triple '%1' is invalid">;
+
+def warn_missing_include_dirs : Warning <
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bradenhelmer wrote:

Tested with GCC, its not enabled in `-Wall` or `-Wextra`, leaving as `DefaultIgnore` for now.

https://github.com/llvm/llvm-project/pull/94827