parser: use Parser.builtin_mod instead of checking p.mod (#8137)

vlib/v/parser/fn.v

@@ -254,7 +254,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		pos := p.tok.position()
 		// TODO high order fn
 		name = if language == .js { p.check_js_name() } else { p.check_name() }
-		if language == .v && !p.pref.translated && util.contains_capital(name) && p.mod != 'builtin' {
+		if language == .v && !p.pref.translated && util.contains_capital(name) && !p.builtin_mod {
 			p.error_with_pos('function names cannot contain uppercase letters, use snake_case instead',
 				pos)
 			return ast.FnDecl{
@@ -270,7 +270,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			}
 		}
 		// cannot redefine buildin function
-		if !is_method && p.mod != 'builtin' && name in builtin_functions {
+		if !is_method && !p.builtin_mod && name in builtin_functions {
 			p.error_with_pos('cannot redefine builtin function `$name`', pos)
 			return ast.FnDecl{
 				scope: 0

vlib/v/parser/parse_type.v

@@ -250,7 +250,7 @@ pub fn (mut p Parser) parse_any_type(language table.Language, is_ptr bool, check
 		name = p.expr_mod + '.' + name
 	} else if name in p.imported_symbols {
 		name = p.imported_symbols[name]
-	} else if p.mod != 'builtin' && name.len > 1 && name !in p.table.type_idxs {
+	} else if !p.builtin_mod && name.len > 1 && name !in p.table.type_idxs {
 		// `Foo` in module `mod` means `mod.Foo`
 		name = p.mod + '.' + name
 	}

vlib/v/parser/struct.v

@@ -65,9 +65,7 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 		p.error('`$p.tok.lit` lacks body')
 		return ast.StructDecl{}
 	}
-	if language == .v &&
-		p.mod != 'builtin' && name.len > 0 && !name[0].is_capital() && !p.pref.translated
-	{
+	if language == .v && !p.builtin_mod && name.len > 0 && !name[0].is_capital() && !p.pref.translated {
 		p.error_with_pos('struct name `$name` must begin with capital letter', name_pos)
 		return ast.StructDecl{}
 	}