Smart SMC syntax for `jr`

[formicant]

In version 1.21.0 the label+* syntax works for most instructions but does not for jr.
Self-modified jrs are useful sometimes.

; Shifts `b` by (7 -`a`) bits to the left
left_shift:
        ld (.bits), a
        ld a, b
.bits+1 jr $    ; works
;.bits+* jr $   ; error:
                ;  unresolved smart-SMC symbol
                ;  (no significant target)
    .7  add a, a
        ld b, a
        ret

[formicant]

Also, djnz.