ee9ccdf6 "reduce cost of ProfileZone when it is
not active" had changed g_bRecording from a bool guarded by g_aMutex to a
volatile bool.  But having been guarded by a mutex indicates that g_bRecording
is potentially accessed from multiple threads, and volatile does not avoid
races.

Change-Id: I933ff5d912cbc7acce52155c605d9c19049c66aa
Reviewed-on: https://gerrit.libreoffice.org/63073Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>