Assert that ValueHandleBase::ValueIsRAUWd doesn't change the tracked Value type.

This invariant is enforced in Value::replaceAllUsesWith, thus it seems
logical to apply it also to ValueHandles. This commit fixes InstCombine
to not trigger the assertion during the removal of constant bitcasts in
call instructions.

Differential Revision: http://reviews.llvm.org/D5828

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220468 91177308-0d34-0410-b5e6-96231b3b80d8