Ban sequentially consistent with VulkanKHR
* Added validation check that SequentiallyConsistent memory semantics
are not used if the memory model is VulkanKHR
* Added tests
* Fixed a bug in evaluating constant 32-bit integers and updated some
handling to avoid inferring a value from a spec constant default
Remaining memory semantics validation
* Adds checks that OutputMemoryKHR, MakeAvailableKHR and MakeVisibleKHR
are only used if the VulkanMemoryModelKHR capabailty is present
* Added checks that MakeAvailableKHR requires release semantics
* Added checks that MakeVisibleKHR requires acquire semantics
* Added checks that MakeAvailableKHR and MakeVisibleKHR require a
storage class
* Replaced uses in opcode validation of current_function()
* Added non-const accessor to function lookup in ValidationState_t
* Updated a couple bad tests due to check reordering
This CL moves the various validate files into the val/ directory with
the rest of the validation infrastructure. This matches how opt/ is
setup with the passes with the infrastructure.
