Before clang 9, it was enabled by default
when -fsanitize=undefined was set.
Pick-to: 5.15
Change-Id: I0faf3ae1901d4badc6d265fa8081185be4360636
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>