Add some negative (and positive) static_assert checks for ArrayRef-of-pointer conversions introduced in r216709

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216830 91177308-0d34-0410-b5e6-96231b3b80d8
Simplify expression using container's front() rather than begin()->

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216833 91177308-0d34-0410-b5e6-96231b3b80d8