Variables placed on the stack. They allow an indirection
so, that when used in an operation, the correct LLVM type can be inserted.
Attributes:
type: the Numba type (see numba.typesystem and minivect/minitypes)
is_local/is_global/is_constant
name: name of local or global
lvalue: LLVM Value
state: state passed from one stage to the next