uClibc: add linuxthreads/errno fix for snapshot version

See uclibc #2089 for details.

This is still not included upstream, but lets include it anyway as
several people have been running into the issue.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>