FTBFS in mock but not a real EL5 system

[T.C. Hollingsworth]

Hi all!

Node.js upstream recently switched from hardcoding LINUX_VERSION_CODE
to checking that __NR_accept4 is defined when checking that the
"accept4" syscall is available. (see patch here [1])

This breaks building for EL5 in mock on F16 (see log tail here [2]),
but not on a real CentOS 5 system.  A quick grep of
$MOCK_ROOT/usr/include indicates that __NR_accept4 isn't defined, as
it should be, so I'm not sure what's going wrong here, or if it's a
problem in mock or upstream.

Thanks!
-T.C.

[1] https://github.com/joyent/libuv/commit/d5b26154
[2] http://tchol.org/nodejs/accept4_ftbfs