It serves no purpose nowadays. All vars are aligned to MINT_STACK_SLOT_SIZE.

This will enable us to control alignment of Vector128 vars at compile time.

For normal calls, we introduce a new opcode before the call that will move all the arguments to aligned stack location. When emitting the code for the call, we emit directly the aligned call args offset instead. Unoptimized code has its own opcodes that do moving of param, we tweak them to copy them into aligned location.