bin/run: Adapt to run on Debian so-called GNU/Linux systems too

Amazingly Debian does not ship the realpath(1) from coreutils but has a
separate source package for it, and it's not installed by default.
Use readlink -f instead.

Change-Id: I6e97c851e6ab96dac08771145e2ab39dd9c11c22

bin/run

@@ -30,14 +30,14 @@ exec "${exedir}"/$@
 
 else
 
-dir=$(realpath "$(pwd)")
+dir=$(readlink -f "$(pwd)")
 
 while test ! -d "${dir}/instdir/program" ; do
     if test "${dir}" = "/"; then
         echo "error: cannot find \"program\" dir from \"$(pwd)\""
         exit 1
     fi
-    dir=$(realpath "${dir}/..")
+    dir=$(readlink -f "${dir}/..")
 done
 
 exedir="${dir}"/workdir/LinkTarget/Executable