use MOVZX more for 64 bit code
Add defaultInitLiteral() to TypeVector.

The default init literal of a `TypeVector` element should be an `ArrayLiteralExp` and not a scalar value.
Merge pull request #2283 from redstar/vectorliteral

Add defaultInitLiteral() to TypeVector.
Merge pull request #2273 from WalterBright/use-movzx

use MOVZX more for 64 bit code