Generate debug info for LLDB/GDB (#50)

* Transform DWARF sections into native format for wasm2obj and wasmtime.

Generate DWARF sections based on WASM DWARF.
Ignore some of debug_info/debug_line for dead code.

* Fix test

lib/wast/src/spectest.rs

@@ -223,6 +223,7 @@ pub fn instantiate_spectest() -> Result<InstanceHandle, InstantiationError> {
         imports,
         &data_initializers,
         signatures.into_boxed_slice(),
+        None,
         Box::new(()),
     )
 }