On BSD systems backtrace lies in libexecinfo. Use
FindBacktrace from CMake to be able to resolve
backtrace on more unixes than linux.
Change-Id: Ie14fd1727d2da03645fc2d6de10c0217baabad6b
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
