[Python-buildbots] Add a config for a clang-ubsan buildbot please

The configure command needs to be:

CC=clang LD=clang CFLAGS="-fsanitize=undefined" LDFLAGS="-fsanitize=undefined" ./configure --with-pydebug

I may be offline for a few days, but i'll get this running in the next week or two.

thanks! -gps