compiler: support for -color/-nocolor option overrides

vlib/v/util/errors.v

@@ -30,7 +30,7 @@ pub const (
 )
 
 pub struct EManager {
-pub mut:
+mut:
 	support_color bool
 }
 
@@ -40,6 +40,10 @@ pub fn new_error_manager() &EManager {
 	}
 }
 
+pub fn (e &EManager) set_support_color(b bool) {
+	e.support_color = b
+}
+
 fn bold(msg string) string {
 	if !emanager.support_color {
 		return msg