[clang] [llvm] Enable ClangIR Build By Default (PR #221291)

[Corentin Jabot via cfe-commits]

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@@ -17,13 +12,6 @@ Documents](#clangir-design-documents) for in-depth coverage of CIR's design.
 
 ## Using ClangIR
 
-:::{note}
-Until [#221291](https://github.com/llvm/llvm-project/pull/221291) lands, you
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cor3ntin wrote:

FYI, I did ask Erich to remove that, it's moved to the general build flags documentation

https://github.com/llvm/llvm-project/pull/221291