Fail earlier if Go is not available

builder/build.go

@@ -191,6 +191,9 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	lprogram, err := loader.Load(config, pkgName, config.ClangHeaders, types.Config{
 		Sizes: compiler.Sizes(machine),
 	})
+	if err != nil {
+		return BuildResult{}, err
+	}
 	result := BuildResult{
 		ModuleRoot: lprogram.MainPkg().Module.Dir,
 		MainDir:    lprogram.MainPkg().Dir,
@@ -200,9 +203,6 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		// If there is no module root, just the regular root.
 		result.ModuleRoot = lprogram.MainPkg().Root
 	}
-	if err != nil { // failed to load AST
-		return result, err
-	}
 	err = lprogram.Parse()
 	if err != nil {
 		return result, err