Don't emit empty DWARF sections

[daxpedda]

This change prevents empty custom sections for debug information to be generated when no debug information is available. fallible-iterator is not a new dependency, it is a dependency of gimli, but is not re-exported.

Not only are a bunch of empty custom sections undesirable, seemingly wasm-opt had issues parsing those. I'm unsure if this is a bug or not, I don't know if completely empty DWARF sections are valid or not.

This will enable wasm-bindgen to stop throwing away the debug information if its available.

See rustwasm/wasm-bindgen#3876.

[philipc]

While empty DWARF sections shouldn't be a problem, it's pointless to emit them. This applies even if some DWARF sections have data and others don't. So I think it would be better to skip the following if data is empty:

walrus/src/module/debug/mod.rs

Lines 118 to 121 in 27f6b62

	cx.wasm_module.section(&wasm_encoder::CustomSection {
	name: id.name().into(),
	data: data.slice().into(),
	});

[daxpedda]

While empty DWARF sections shouldn't be a problem, it's pointless to emit them. This applies even if some DWARF sections have data and others don't. So I think it would be better to skip the following if data is empty:

Ha, this is actually what I had implemented initially.
Will do that then, thank you!