codegen: Do generate field offset checks for classes with multiple bases.

The bug only affects virtual inheritance, so instead disable layout
tests in the test that we know is broken. Not generating layout tests is
wrong anyways, because the offset would be wrong.

Author: emilio

bindgen-tests/tests/expectations/tests/inherit_multiple_interfaces.rs

@@ -0,0 +1,15 @@
+class A {
+  virtual void Foo();
+
+  int member;
+};
+
+class B {
+  virtual void Bar();
+
+  void* member2;
+};
+
+class C : public A, public B {
+  float member3;
+};

bindgen-tests/tests/expectations/tests/virtual_inheritance.rs

@@ -1,4 +1,5 @@
-
+// bindgen-flags: --no-layout-tests
+// FIXME: Enable layout tests when #465 is fixed.
 class A {
   int foo;
 };

bindgen-tests/tests/headers/inherit_multiple_interfaces.hpp

@@ -2193,16 +2193,7 @@ impl CodeGenerator for CompInfo {
                         })
                     };
 
-                    // FIXME when [issue #465](https://github.com/rust-lang/rust-bindgen/issues/465) ready
-                    let too_many_base_vtables = self
-                        .base_members()
-                        .iter()
-                        .filter(|base| base.ty.has_vtable(ctx))
-                        .count() >
-                        1;
-
-                    let should_skip_field_offset_checks =
-                        is_opaque || too_many_base_vtables;
+                    let should_skip_field_offset_checks = is_opaque;
 
                     let check_field_offset = if should_skip_field_offset_checks
                     {