This returns the type of data in the Block, which might be different
than the type of the expression or declaration we created the block for.
This lets us remove some special cases from CheckNewDeleteForms() and
CheckNewTypeMismatch().
When creating descriptor for array element types, we only save the
original source, e.g. int[2][2][2]. So later calls to getType() of the
element descriptors will also return int[2][2][2], instead of e.g.
int[2][2] for the second dimension.
Fix this by explicitly tracking the array types.
The last attached test case used to have an lvalue offset of 32 instead
of 24.
We should do this for more desriptor types though and not just composite
array, but I'm leaving that to a later patch.
Note that PointerUnion::dyn_cast has been soft deprecated in
PointerUnion.h:
// FIXME: Replace the uses of is(), get() and dyn_cast() with
// isa<T>, cast<T> and the llvm::dyn_cast<T>
Literal migration would result in dyn_cast_if_present (see the
definition of PointerUnion::dyn_cast), but this patch uses dyn_cast
because we expect Source to be nonnull.
