there is a lot to say about your code but

why should xmt_flag be tested for not being zero in line 36 if its value is known zero?

_uart_send:
        mov     _SBUF,dpl
;       uart.c:31: xmt_flag = 0;
        clr     a
        mov     _xmt_flag,a
        mov     (_xmt_flag + 1),a
;       uart.c:34: while (1)
00105$:
;       uart.c:39: opti_fooler++;
        inc     _opti_fooler
        clr     a
        cjne    a,_opti_fooler,00105$
        inc     (_opti_fooler + 1)
        sjmp    00105$
 

Hint: lookup "volatile", then recheck, then remove the variable:)