[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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@@ -317,6 +317,24 @@ Makes programs 10x faster by doing Special New Thing.
 
 ### Changes to the LLVM tools
 
+* llvm-ml now supports the `/unwindv3` flag to enable V3 unwind information
+  format for x64 exception handling.
+* llvm-ml now supports the `@UnwindVersion` built-in symbol, which returns the
+  current unwind version (1 by default, 3 when `/unwindv3` is specified).
+* llvm-ml now supports the `.push2reg`, `.pop2reg`, `.beginepilog`, and
+  `.endepilog` MASM directives for V3 unwind information.
+* llvm-ml now supports the `.popreg`, `.freestack`, `.restorereg`,
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mikolaj-pirog wrote:

Aren't these only valid for v3?

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