Gets the built-in
expr has an lvalue-to-rvalue conversion that should be ignored when generating IR. This occurs for conversion from an lvalue of function type to an rvalue of function pointer type. The conversion is represented in the AST as an lvalue-to-rvalue conversion, but the IR represents both a function lvalue and a function pointer prvalue the same.
expr is a constant of a type that can be replaced directly with its value in the IR. This does not include address constants as we have no means to express those as QL values.