When running wasm-opt, ignore any failure because it will fail for unknown flags...

When running wasm-opt, ignore any failure because it will fail for unknown flags and the set of legal flags will change from version to version.  Document the size-reduction effect (or non-effect) of a dozen-odd wasm-opt flags and retain those which demonstrate a wasm file size reduction in -Oz builds (our production build mode). Total size savings: roughly 13kb.

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