DISCLAIMER: this is on a crunchbang 11 box - I don't have a native 64-bit Ubuntu box to check
I *think* that the link gets created when you install the i386 libc6-dev packages e.g.
Then if I do
$ apt-cache policy libc6-dev-i386
500 http://ftp.debian.org/debian/ wheezy/main amd64 Packages
$ find /usr/include/sys -name 'types.h'
Obviously that brings in a whole multilib infrastructure - I don't *think* that's a problem, but ymmv
$ sudo apt-get install libc6-dev-i386
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
The following NEW packages will be installed:
0 upgraded, 2 newly installed, 0 to remove and 59 not upgraded.
Need to get 5,620 kB of archives.
After this operation, 14.7 MB of additional disk space will be used.
Do you want to continue [Y/n]?
Get:1 http://ftp.debian.org/debian/ wheezy/main libc6-i386 amd64 2.13-38 [4,033 kB]
Get:2 http://ftp.debian.org/debian/ wheezy/main libc6-dev-i386 amd64 2.13-38 [1,586 kB]
Fetched 5,620 kB in 4s (1,405 kB/s)
Selecting previously unselected package libc6-i386.
(Reading database ... 145080 files and directories currently installed.)
Unpacking libc6-i386 (from .../libc6-i386_2.13-38_amd64.deb) ...
Selecting previously unselected package libc6-dev-i386.
Unpacking libc6-dev-i386 (from .../libc6-dev-i386_2.13-38_amd64.deb) ...
Setting up libc6-i386 (2.13-38) ...
Setting up libc6-dev-i386 (2.13-38) ...
$ find /usr/include/sys -name 'types.h' -ls
1452115 0 lrwxrwxrwx 1 root root 31 Dec 30 10:37 /usr/include/sys/types.h -> ../x86_64-linux-gnu/sys/types.h