I finally got all needed library to build in debug and being used by the game!
I followed the instruction on this page:
http://x.debian.net/howto/build-mesa.html with the exception of
"--with-dri-drivers=r600" that didn't work but I guess it is not important as
gallium is standard now for r600, and the addition of "--enable-debug".

However with those debug libraries I do not get the crash at the very same
moment, but something like one second later. However it is the  same kind of
problem: a read access made too far from the source buffer (I'll attach the
call stack again). This time a memcpy of 520 bytes is attempted from a buffer
of 512 bytes. Now that I can do step by step debugging with all symbols
identified by gdb I will try to understand what's happening.