[clang] [clang]: implement std::meta::is_type (PR #211653)

[Ambrose Leeb via cfe-commits]

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@@ -25,6 +25,24 @@
 // precxx20-error at -3 {{does not have the constexpr builtin}}
 // c-error at -4 {{does not have the constexpr builtin}}
 
+#if __has_builtin(__builtin_meta_is_type)
+#error has the builtin
+#else
+#error does not have the builtin
+#endif
+// cxx20-cxx26-error at -4 {{has the builtin}}
+// precxx20-error at -3 {{does not have the builtin}}
+// c-error at -4 {{does not have the builtin}}
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Sirraide wrote:

Well, the metafunctions are only useful w/ reflection, which we’re almost certainly going to guard behind C++26, so yeah, I think we should just require C++26 (as well as `-freflection` currently) for all of them

https://github.com/llvm/llvm-project/pull/211653