Explicitly search for libxml2 to ensure the version shipped with the LCG is used.
When building on plus (online), the system version was picked up, which lead to silent segfaults when generating headers using god.py.
MR for master: !589 (merged)
When building on plus (online), the system version was picked up, which lead to silent segfaults when generating headers using god.py.
MR for master: !589 (merged)