[pic16] --stack-auto with sdcclib

Hello,
I found that using --stack-auto when (re)compiling sdcclib for needed
reetrancy (as manual recommends) can break int (and long)
multiplication in "user" code when interrupts are on.
And not only int/long, libmath too.
Looks like an "empty" ISR (which has only a prologue and epilogue) has
impact on _mulint result and using simple code:
volatile int x;

int main(){
while(1){
x=100;
x=x*x; // <x becomes not 10000 when ISR is active
}

When I disable interrupts at the end of _mulint reentrant code:
[...]
    BCF _INTCONbits,7
    MOVFF   PREINC1, r0x09
    MOVFF   PREINC1, r0x08
    MOVFF   PREINC1, r0x07
    MOVFF   PREINC1, r0x06
    MOVFF   PREINC1, r0x05
    MOVFF   PREINC1, r0x04
    MOVFF   PREINC1, r0x03
    MOVFF   PREINC1, r0x02
    MOVFF   PREINC1, r0x01
    MOVFF   PREINC1, r0x00
    MOVWF   POSTINC1
    MOVLW   0x05