constexpr: don't consider class types with mutable members to be literal types.

The standard doesn't allow this, but mutable constexpr variables break the
semantics so badly that we can't reasonably accept them.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@141768 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed