[Bug libstdc++/103891] clang-13 fails to compile libstdc++'s std::variant>: error: attempt to use a deleted function

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103891

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I suppose we could just do:

--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -54,7 +54,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION

-#if __cplusplus >= 202002L && __cpp_concepts
+#if __cplusplus >= 202002L && __cpp_concepts && __GNUC__ >= 12
 // P2231R1 constexpr needs constexpr unions and constrained destructors.
 # define __cpp_lib_variant 202106L
 #else

And then improve it later if GCC updates __cpp_concepts