My apologies for the horrible patch.
The code in LLDB assumes that CompilerType and friends use the size 0 as a sentinel value to signal an error. This works for C++, where no zero-sized type exists, but in many other programming languages (including I believe C) types of size zero are possible and even common. This is a particular pain point in swift-lldb, where extra code exists to double-check that a type is *really* of size zero and not an error at various locations.
To remedy this situation, this patch starts by converting CompilerType::getBitSize() and getByteSize() to return an optional result. To avoid wasting space, I hand-rolled my own optional data type assuming that no type is larger than what fits into 63 bits. Follow-up patches would make similar changes to the ValueObject hierarchy.