make "unreachable code" a warning in non-prod builds

vlib/compiler/aparser.v

@@ -1424,7 +1424,7 @@ fn (p mut Parser) gen(s string) {
 fn (p mut Parser) statement(add_semi bool) string {
 	p.expected_type = ''
 	if p.returns {
-		p.error('unreachable code')
+		p.warn_or_error('unreachable code')
 	}
 	// if !p.in_dispatch {
 	p.cgen.is_tmp = false

vlib/v/fmt/tests/simple_expected.vv

@@ -76,6 +76,5 @@ fn get_user() ?User {
 
 fn get_user_ptr() &User {
 	return &User{
-
 	}
 }