Fix PR#20834 - 'is_trivially_destructible yeilds wrong answer for arrays of unknown bound' Thanks to K-ballo for the bug report. Update a few of the other tests while we're here, and fix a typo in a test name.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@216909 91177308-0d34-0410-b5e6-96231b3b80d8