cgen,markused: remove unused enum declarations too (#25033)

cmd/tools/vast/vast.v

@@ -729,6 +729,7 @@ fn (t Tree) enum_decl(node ast.EnumDecl) &Node {
 	obj.add('comments', t.array_node_comment(node.comments))
 	obj.add_terse('attrs', t.array_node_attr(node.attrs))
 	obj.add_terse('typ', t.type_node(node.typ))
+	obj.add_terse('enum_typ', t.type_node(node.enum_typ))
 	return obj
 }
 

vlib/v/ast/ast.v

@@ -1475,6 +1475,8 @@ pub:
 	typ              Type        // the default is `int`; can be changed by `enum Big as u64 { a = 5 }`
 	typ_pos          token.Pos
 	pos              token.Pos
+pub mut:
+	enum_typ Type
 }
 
 pub struct AliasTypeDecl {

vlib/v/checker/checker.v

@@ -2161,6 +2161,7 @@ fn (mut c Checker) enum_decl(mut node ast.EnumDecl) {
 			}
 		}
 	}
+	node.enum_typ = c.table.find_type_idx(node.name)
 }
 
 fn (mut c Checker) check_enum_field_integer_literal(expr ast.IntegerLiteral, is_signed bool, is_multi_allowed bool,

vlib/v/gen/c/cgen.v

@@ -4771,7 +4771,7 @@ fn (mut g Gen) enum_decl(node ast.EnumDecl) {
 		}
 		return
 	}
-	if g.pref.skip_unused && node.typ.idx() !in g.table.used_features.used_syms {
+	if g.pref.skip_unused && node.enum_typ !in g.table.used_features.used_syms {
 		return
 	}
 	g.enum_typedefs.writeln('')

vlib/v/markused/walker.v

@@ -846,7 +846,7 @@ fn (mut w Walker) expr(node_ ast.Expr) {
 					w.expr(filtered[0].expr)
 				}
 			}
-			w.mark_by_sym_name(node.enum_name)
+			w.mark_by_type(node.typ)
 		}
 		ast.LockExpr {
 			w.uses_lock = true