Java 8 rules for method overrides:

- base class method wins against a (default) interface method,
so an abstract base class method should always be implemented
in a derived class;

- interface methods clash regardless of abstract/default
with possibly undefined behavior at run-time,
so a class or interface should always define its own method
for methods inherited from multiple interfaces and not from base class;

- meaningful diagnostics for class inheriting conflicting JVM signatures.
Since no override will happen under Java 8 rules,
ACCIDENTAL_OVERRIDE is misleading for this case;

- update testData.

compiler/testData/codegen/bytecodeText/interfaces/firstInheritedMethodIsAbstract.kt

@@ -6,7 +6,9 @@ interface B {
     fun foo(): String = "OK"
 }
 
-interface C : A, B
+interface C : A, B {
+    override fun foo(): String = super<B>.foo()
+}
 
 // There's no 'foo' in A$DefaultImpls, proguard and other tools may fail if we generate calls to it
 // 0 INVOKESTATIC A\$DefaultImpls.foo