Running `wasm-opt` with `-Os` leaves NOP / dead control flow behind

See attached flute.tar.gz

We start with an unoptimized flute.wasm file and run wasm-opt

% wasm-opt -g --enable-gc --enable-reference-types --enable-multivalue --enable-exception-handling --enable-nontrapping-float-to-int --enable-sign-ext --enable-bulk-memory --enable-threads '--no-inline=*<noInline>*' --traps-never-happen \
    -Os \
    flute.wasm \
    -o flute.Os.wasm

This -Os leaves NOP blocks behind:

 (func $_InterfaceType.toString ...
  ...
    block $label0 (result i32)
      local.get $var0
      ref.cast $_InterfaceType
      local.tee $var7
      struct.get $_InterfaceType $classId
      br $label0
    end $label0
  ...
)

It also doesn't prune branches with unreachable (some variants of this):

(func $_FunctionType.toString
  ...
            if (result (ref $JSStringImpl))
              local.get $var6
              unreachable
            else
              local.get $var6
              block $label5 (result (ref $JSStringImpl))
                local.get $var9
                i32.const 0
                global.get $"C8 DiagnosticLevel"
                ref.null none
                local.get $var9
                struct.get $_Type $field0
                i32.const 3066
                i32.add
                call_indirect (param (ref $#Top) i32 (ref $DiagnosticLevel) (ref null $TextTreeConfiguration)) (result (ref $JSStringImpl))
                br $label5
              end $label5
              call $JSStringImpl.+
            end
  ...  
)

If we run another -Os pass then those issues disappear

% wasm-opt -g --enable-gc --enable-reference-types --enable-multivalue --enable-exception-handling --enable-nontrapping-float-to-int --enable-sign-ext --enable-bulk-memory --enable-threads '--no-inline=*<noInline>*' --traps-never-happen \
    -Os \
    flute.Os.wasm \
    -o flute.Os.Os.wasm

From a users point of view, I wouldn't expect an -Os to leave these code patterns behind. We can of course run multiple -Os rounds, but that a) may do more work than needed and b) raises the question of how many -Os passes one may need to run to cleanup things left by previous -Os passes.

Start by reproducing the report with the attached flute.wasm and the shown wasm-opt command, then inspect the first -Os output for the NOP blocks and unreachable branches shown in the issue. Compare it with a second -Os pass; done means one optimization pass removes these dead control-flow patterns without requiring repeated -Os runs.