ARC: nptl: cancellable wrappers were broken

ARC: nptl: cancellable wrappers were broken

This was reported as uClibc test suite failures of tst-mqueue3 and
tst-mqueue5.

The syscall args were getting clobbered, so use scratch regs which are
not used for syscall args

00002690 <mq_timedsend>:

    ; SINGLE_THREAD_P

    2690:	sub	r1,r25,0x448   <--- clobers r1, r2
    2698:	ld	r2,[r1]
    269c:	cmp	r2,0

    26a0:	bz	mq_timedsend_nocancel

    ; DOCARGS (saves syscall args but r1, r2 clobbered already)

    26a4:	st.aw	blink,[sp,-4]
    26a8:	st.aw	r0,[sp,-4]
    26ac:	st.aw	r1,[sp,-4]
    26b0:	st.aw	r2,[sp,-4]
    26b4:	st.aw	r3,[sp,-4]
    26b8:	st.aw	r4,[sp,-4]
    26bc:	bl	1e28 <__librt_enable_asynccancel>

Reported-by: Eugeniy Paltsev <paltsev@synopsys.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>