Add an assertion to the form of SelectionDAG::getConstant that takes

Add an assertion to the form of SelectionDAG::getConstant that takes
a uint64_t to verify that the value is in range for the given type,
to help catch accidental overflow. Fix a few places that relied on
getConstant implicitly truncating the value.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63128 91177308-0d34-0410-b5e6-96231b3b80d8