tst-preadvwritev, tst-preadvwritev64 failing for MIPS n32

[Joseph Myers]

With the consolidated preadv and pwritev implementations, I see

FAIL: misc/tst-preadvwritev
FAIL: misc/tst-preadvwritev64

for MIPS n32 (note: since these are new tests I haven't confirmed whether 
the problem was actually introduced by the consolidation, or present 
before).  The failures are:

error: first PWRITEV returned -1 (line 70)

Note: for these syscalls n32 uses the compat implementation in the kernel 
(as required to use the compat iovec structure), meaning the off_t 
arguments are passed in two separate registers.

-- 
Joseph S. Myers
joseph@codesourcery.com