[clang] [Clang] Add __builtin_bswapg (PR #162433)

[Nikolas Klauser via cfe-commits]

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@@ -12951,6 +12951,9 @@ def err_builtin_invalid_arg_type: Error<
   "%plural{0:|: }3"
   "%plural{[0,3]:type|:types}1 (was %4)">;
 
+def err_bswapg_bitint_not_16bit_aligned : Error<
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philnik777 wrote:

You want to use the `g` version, but that still behaves the same: https://godbolt.org/z/eaMjfW57K - so yeah, I think we should stay consistent here and swap the underlying type.

https://github.com/llvm/llvm-project/pull/162433