Support six-argument syscalls from C for 32-bit x86, use generic lowlevellock-futex.h (bug 18138)

[Joseph Myers]

On Mon, 23 Mar 2015, Carlos O'Donell wrote:

> Thanks, I'm OK with this patch as-is then.

I've committed this patch.  If anyone wishes to make further refinements 
to the approach for six-argument syscalls, such refinements are welcome 
(and I think the glibc testsuite provides adequate coverage through the 
NPTL tests).

-- 
Joseph S. Myers
joseph@codesourcery.com