I succesfully used Alien Bob's multilib environment in Slackware for a long time. Recently I upgraded kernel+glibc+gcc Slackware packages which rewrote installed multilib gcc/glibc and I tried to rebuild Alien Bob's multilib toolchain for Slackware from scratch according to Alien Bob's description README but I was not succesfull. The change I made in existing Alien Bob's SlackBuild scripts was to compile gcc-4.4.3 instead of gcc-4.3.3.

First issue was that glibc.pthread-disable-forced-unwind-check.diff.gz patch was not applicable to glibc-2.11.1 sources and glibc-multilib.SlackBuild script failed. I was able to make my own patch that solves this issue and I was able to create "bootstrap" version of a multilib glibc.

Second issue is that I'm not able to use temporary gcc/glibc bootstrap toolchain to build a shared, multilib set of packages for the "c,c++,ada" languages by using gcc-multilib.SlackBuild script. During gcc configuration configuration script says that gcc is not able to compile ada. I'm confusing by Alien Bob's sentence in description "The pre-existing gnat compiler will be used by the static gcc to recompile gnat for multilib.". It seems that static gcc compiler is not able to use pre-existing gnat compiler from default Slackware installation. I extracted source file and test for ada from gcc configuration script and run
or
both say that ada is not supported by gcc that is probably right because static gcc doesn't support ada.

My question is how to build a shared, multilib set of packages for the "c,c++,ada" languages and proceed to following step and rebuild glibc packages.

Thank you for any help or explanation.

It was hard enough building the multilib toolchain from scratch the first time! So, I will not try to replay it and see how I can resolve your errors ;-)
There's simply not enough time.

What you should do once you have a working set of multilib gcc and glibc packages, is to use those to build never versions of them.

Eric