Properly handle instantiation-dependent array bounds.

Properly handle instantiation-dependent array bounds.

We previously failed to treat an array with an instantiation-dependent
but not value-dependent bound as being an instantiation-dependent type.
We now track the array bound expression as part of a constant array type
if it's an instantiation-dependent expression.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@373685 91177308-0d34-0410-b5e6-96231b3b80d8