Commit 78345c68 makes at least gcc 4.1.2 on RHEL 5 complain:

cc1: warnings being treated as errors
In file included from vbox/vbox_V4_0.c:13:
vbox/vbox_tmpl.c: In function 'vboxDomainUndefineFlags':
vbox/vbox_tmpl.c:5298: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]

* src/vbox/vbox_tmpl.c (vboxDomainUndefineFlags): Use union to
avoid compiler warning.