Fix missing-prototypes

xfce-notify-log.c:406:6: error: no previous prototype for 'xfce_notify_clear_icon_cache' [-Werror=missing-prototypes]

Signed-off-by: Olaf Hering <olaf@aepfle.de>
2 jobs for !15 with missing-prototypes in 1 minute and 17 seconds (queued for 3 seconds)
detached
Status Job ID Name Coverage
  Build
passed #9803
build

00:00:31

 
  Distcheck
passed #9804
distcheck

00:00:46