When checking overrides, compare methods structurally

Because they may come from different copies of the same class from different modules

compiler/testData/diagnostics/tests/multimodule/duplicateMethod/simpleWithInheritance.kt

@@ -0,0 +1,38 @@
+// MODULE: m1
+// FILE: a.kt
+package p
+
+public trait B {
+    public fun getParent(): B?
+}
+
+// MODULE: m2(m1)
+// FILE: b.kt
+package p
+
+public trait C : B {
+    override fun getParent(): B?
+
+}
+
+// MODULE: m3
+// FILE: b.kt
+package p
+
+public trait B {
+    public fun getParent(): B?
+}
+
+public trait D : B {
+    override fun getParent(): B?
+}
+
+// MODULE: m4(m3, m2)
+// FILE: c.kt
+import p.*
+
+fun test(b: B?) {
+    if (b is C && b is D) {
+        b?.<!OVERLOAD_RESOLUTION_AMBIGUITY!>getParent<!>()
+    }
+}