[clang] [clang] Reject character devices in #embed for now (PR #135370)

[via cfe-commits]

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@@ -458,6 +458,8 @@ def warn_compat_pp_embed_directive : Warning<
   InGroup<CPre23Compat>, DefaultIgnore;
 def err_pp_embed_dup_params : Error<
   "cannot specify parameter '%0' twice in the same '#embed' directive">;
+def err_pp_embed_device_file : Error<
+  "device files are not yet supported by '#embed' directive">;
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cor3ntin wrote:

```suggestion
def err_pp_embed_device_file : Error<
  "device files are not supported by '#embed' directive">;
```

Can we remove `yet`? It's unclear that it's a direction that we will ever want to go in, and I don't want to set the wrong expectations

https://github.com/llvm/llvm-project/pull/135370