[llvm] [Flang-rt][build] fixes building warnings under gcc: (PR #173955)

[Eugene Epshteyn via llvm-commits]

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@@ -67,7 +67,7 @@ struct MaxOrMinIdentity<TypeCategory::Real, 16, IS_MAXVAL,
     // Create a buffer to store binary representation of __float128 constant.
     constexpr std::size_t alignment =
         std::max(alignof(Type), alignof(std::uint64_t));
-    alignas(alignment) char data[sizeof(Type)];
+    alignas(alignment) char data[sizeof(Type)]{};
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eugeneepshteyn wrote:

I don't think this is necessary, because `data` is completely assigned to below. Adding default initialization would just initialize `data` to all zeros and then immediately overwrite it below.

https://github.com/llvm/llvm-project/pull/173955