cgen: fix gen of `>` operator overloading (#8600)

vlib/v/gen/c/cgen.v

@@ -3378,14 +3378,18 @@ fn (mut g Gen) infix_expr(node ast.InfixExpr) {
 			g.write(')')
 		} else if node.op in [.ne, .gt, .ge, .le] && ((a && b && e) || c || d) {
 			typ := g.typ(if !d { left_type } else { (left_sym.info as table.Alias).parent_type })
-			g.write('!$typ')
+			if node.op == .gt {
+				g.write('$typ')
+			} else {
+				g.write('!$typ')
+			}
 			g.write('_')
 			if node.op == .ne {
 				g.write('_eq')
 			} else if node.op in [.ge, .le, .gt] {
 				g.write('_lt')
 			}
-			if node.op == .le {
+			if node.op in [.le, .gt] {
 				g.write('(')
 				g.expr(node.right)
 				g.write(', ')

vlib/v/tests/operator_overloading_cmp_test.v

@@ -0,0 +1,25 @@
+struct Foo {
+	i int
+}
+
+fn (a Foo) < (b Foo) bool {
+	return a.i < b.i
+}
+
+fn (a Foo) == (b Foo) bool {
+	return a.i == b.i
+}
+
+fn test_operator_overloading_cmp() {
+	a := Foo{i: 38}
+	b := Foo{i: 38}
+
+	assert (a > b) == false
+	assert (a < b) == false 
+	//// /// //
+	assert a >= b
+	assert a <= b
+	//// /// //
+	assert b >= a
+	assert b <= a
+}