Support SSA transform

[bspaans]

Support SSA transform in the IR

Expressions:

• and.go
• arithmetic.go
• array_index.go
• bool.go
• byte_array.go
• call.go
• cast.go
• div.go
• equals.go
• float64.go
• function.go
• gte.go
• gt.go
• int16.go
• int32.go
• int64.go
• int8.go
• lte.go
• lt.go
• mul.go
• not.go
• operator.go
• or.go
• static_array.go
• struct_field.go
• struct.go
• syscall.go
• uint16.go
• uint32.go
• uint64.go
• uint8.go
• variable.go

Statements:

• and_then.go
• array_assignment.go
• assignment.go
• function_def.go
• if.go
• return.go
• while.go