This PR adds SPIR-V extension SPV_INTEL_variable_length_array that allows to allocate local arrays whose number of elements is unknown at compile time: * add a new SPIR-V internal intrinsic:int_spv_alloca_array * legalize G_STACKSAVE and G_STACKRESTORE * implement allocation of arrays (previously getArraySize() of AllocaInst was not used) * add tests