[clang] [Clang] Add __has_target_builtin macro (PR #126324)

[Erich Keane via cfe-commits]

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@@ -1819,8 +1822,12 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
               // usual allocation and deallocation functions. Required by libc++
               return 201802;
             default:
+              // __has_target_builtin should return false for aux builtins.
+              if (IsHasTargetBuiltin &&
+                  getBuiltinInfo().isAuxBuiltinID(BuiltinID))
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erichkeane wrote:

This logic doesn't seem right to me.  What happens if this builtin is supported on BOTH the host and device here?  Shouldn't we still return 'true'? 

https://github.com/llvm/llvm-project/pull/126324