[flang] [llvm] [openmp] [Flang-RT] Fix GCC 15.1 Fortran Runtime libstdc++ Undefined Symbols (PR #157385)

[Patrick Simmons via llvm-commits]

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@@ -24,6 +24,9 @@ using cuda::std::variant_size_v;
 using cuda::std::visit;
 } // namespace std
 #else // !RT_USE_LIBCUDACXX
+#include <initializer_list>
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linuxrocks123 wrote:

@Meinersbur I don't see a way to do that because, if we define first, and then `bits/c++config` gets `#include`d, it won't matter that we defined first since, by GCC standards, the most recent definition of a macro controls:

https://gcc.gnu.org/onlinedocs/cpp/Undefining-and-Redefining-Macros.html

(By language standards, it's just undefined behavior, but I think everyone does the same thing as GCC in practice.)

https://github.com/llvm/llvm-project/pull/157385