Harden variant test added in r366022

The test was brittle since it only went boom for one specific type, when
really it should go boom for all of them.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@366025 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed