I just installed Ubuntu 12.04 on a USB stick out of curiosity and started some development and noticed, that /usr/include/sys/, a heavily important directory for POSIX compliant programming, was empty! Some digging revealed that the files I was looking for where located under /usr/include/i386-linux-gnu/sys/ instead.
So what do we do to fix this? I just copied everyting from /usr/include/sys/ to /usr/include/i386-linux-gnu/sys/ (asoundlib.h in my case)
sudo cp /usr/include/sys/* i386-linux-gnu/sys/
Then I deleted that folder
sudo rm -r /usr/include/sys/
And finally made a symlink to that other /sys/
sudo ln -s /usr/include/i386-linux-gnu/sys/ /usr/include/sys