More tests.

test/libsolidity/syntaxTests/inheritance/override/nonintermediate_common_base_and_unique_implementation_modifier.sol

@@ -0,0 +1,17 @@
+contract I {
+	modifier f() { _; }
+}
+contract J {
+	modifier f() { _; }
+}
+contract IJ is I, J {
+	modifier f() virtual override (I, J) { _; }
+}
+contract A is IJ
+{
+	modifier f() override { _; }
+}
+contract B is IJ
+{
+}
+contract C is A, B {}

test/libsolidity/syntaxTests/inheritance/override/override_modifier_no_override.sol

@@ -0,0 +1,7 @@
+abstract contract A {
+}
+abstract contract X is A {
+	modifier f() override { _; }
+}
+// ----
+// TypeError: (65-73): Modifier has override specified but does not override anything.