[llvm] [llvm-ml] Add MASM unwind v3 support for x64 exception handling and improve MSVC compat (PR #202809)

[Mikołaj Piróg via llvm-commits]

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@@ -41,6 +41,8 @@ def fatal_warnings : LLVMFlag<"fatal-warnings">,
                      HelpText<"Treat warnings as errors">;
 def filetype : LLVMJoined<"filetype=">, Values<"obj,s,null">,
                HelpText<"Emit a file with the given type">;
+def mattr : LLVMCommaJoined<"mattr=">,
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mikolaj-pirog wrote:

Why is this needed?

https://github.com/llvm/llvm-project/pull/202809