Currently, WASM symbols taken from the export section of shared objects
lose their flags. This can result in link failures. For example, if a
TLS symbol is exported from a shared object, relocation fails because
`wasm-ld` thinks that the symbol is not flagged as a TLS symbol.
This PR populates symbol flags for symbols in the export section from
the flags stored in the dylink0 section.
The export info section was also not serialized by the WASM emitter for
YAML, which this PR fixes
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