[clang] [Clang] Backport P2741R3 (static_assert with user-generated message) to C++11 (PR #102044)

[Vlad Serebrennikov via cfe-commits]

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@@ -134,7 +134,7 @@ void test() {
 }
 
 namespace cwg2798 { // cwg2798: 17
-#if __cpp_static_assert >= 202306
+#if __cplusplus > 202302L
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Endilll wrote:

Yeah, checking for `__cplusplus` makes more sense in DR test suite.
But I wonder if we can leverage feature test macros for a future conformance testing outside of DRs.

https://github.com/llvm/llvm-project/pull/102044