[toolchain] uClibc: fix uClibc implementation of eventfd

[toolchain] uClibc: fix uClibc implementation of eventfd

uClibc declares eventfd() as taking two arguments but doesn't properly
pass the second argument to the kernel.

The problem is discussed at:
http://lists.uclibc.org/pipermail/uclibc/2012-May/046873.html

This patch is taken from uclibc 0.9.33 git, so will presumably
be integrated in any future releases.

Signed-off-by: Andy Leiserson <andy@leiserson.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@33478 3c298f89-4303-0410-b956-a3cf2f4a3e73