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

tests/instantiate.rs

@@ -42,6 +42,6 @@ fn test_environ_translate() {
     let mut resolver = NullResolver {};
     let mut compiler = Compiler::new(isa);
     let global_exports = Rc::new(RefCell::new(HashMap::new()));
-    let instance = instantiate(&mut compiler, &data, &mut resolver, global_exports);
+    let instance = instantiate(&mut compiler, &data, &mut resolver, global_exports, false);
     assert!(instance.is_ok());
 }