Old gcc complains about shadowing 'sync' variable:

../../src/qemu/qemu_agent.c: In function 'qemuAgentSetTime':
../../src/qemu/qemu_agent.c:1737: warning: declaration of 'sync'
  shadows a global declaration [-Wshadow]
/usr/include/unistd.h:464: warning: shadowed declaration is here
  [-Wshadow]
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>