[llvm] Reapply "Allow "[[FLAGS=<none>]]" value in the ELF Fileheader Flags field (#143845)" (PR #151094)

[Jacob Lambert via llvm-commits]

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@@ -1160,7 +1160,7 @@ void MappingTraits<ELFYAML::FileHeader>::mapping(IO &IO,
   IO.mapOptional("ABIVersion", FileHdr.ABIVersion, Hex8(0));
   IO.mapRequired("Type", FileHdr.Type);
   IO.mapOptional("Machine", FileHdr.Machine);
-  IO.mapOptional("Flags", FileHdr.Flags, ELFYAML::ELF_EF(0));
+  IO.mapOptional("Flags", FileHdr.Flags);
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lamb-j wrote:

This is an addition from the original PR applied right? How does this fix the test failures?

https://github.com/llvm/llvm-project/pull/151094