add wasm-abi field in TargetSpec && set generic for WASI by default (#1421)

Signed-off-by: mathetake <takeshi@tetrate.io>

builder/build.go

@@ -79,7 +79,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 	// keep functions interoperable, pass int64 types as pointers to
 	// stack-allocated values.
 	// Use -wasm-abi=generic to disable this behaviour.
-	if config.Options.WasmAbi == "js" && strings.HasPrefix(config.Triple(), "wasm") {
+	if config.WasmAbi() == "js" {
 		err := transform.ExternalInt64AsPtr(mod)
 		if err != nil {
 			return err