Georg Schwarz wrote:

> No, because that file/symlink does not exist in /usr/X11R6/lib in the first
> place.

With a rather minimalistic installation of Debian, I have not a single
*.so file in /usr/X11R6.
Judging from a past experience with libncurses5 where I was missing
/usr/lib/libncurses.so until I installed libncurses5-dev, you need some
*-dev package.

A short look at the system shows that xlibs-dev will pull in many other
*-dev packages, among them libsm-dev which contains a symlink libSM.so.

ciao
     Klaus