[clang] [clang] Add per-global code model attribute (PR #72078)

[Fangrui Song via cfe-commits]

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@@ -3408,6 +3408,8 @@ def warn_objc_redundant_literal_use : Warning<
 def err_attr_tlsmodel_arg : Error<"tls_model must be \"global-dynamic\", "
   "\"local-dynamic\", \"initial-exec\" or \"local-exec\"">;
 
+def err_attr_codemodel_arg : Error<"code_model '%0' is not yet supported on this target">;
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MaskRay wrote:

We should remove `yet`, because a target may decide not to support the attribute.

The AIX err below is for progress tracking.

https://github.com/llvm/llvm-project/pull/72078