In a Ubuntu Xenial build environment, the compiler identified as
g++-5.real (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
seems to be emitting incorrect code for the compilation unit
trx0rec.cc, triggering a bogus-looking AddressSanitizer report
of an invalid read of something in the function trx_undo_rec_get_pars().
This is potentially affecting any larger tests where the InnoDB
purge subsystem is being exercised.

When the optimization level of trx0rec.cc is limited to -O1, no
bogus failure is being reported. With -O2 or -O3, a lot of things
seemed to be inlined in the function, and the disassembly of the
generated code did not make sense to me.