[llvm] [WebAssembly] Misc. fixes in CFGStackify (PR #107182)

[Heejin Ahn via llvm-commits]

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@@ -293,7 +294,7 @@ void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) {
     }
   }
 
-  // Decide where in Header to put the BLOCK.
+  // Decide where in MBB to put the BLOCK.
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aheejin wrote:

The relevant variable's name is not `Header` but `MBB`. There are several more fixes on this below.

https://github.com/llvm/llvm-project/pull/107182