Fix compilation with -fno-common or gcc10
https://bugs.gentoo.org/706742
--- a/nvidia-settings/src/gtk+-2.x/ctkvdpau.c
+++ b/nvidia-settings/src/gtk+-2.x/ctkvdpau.c
@@ -105,2 +105,4 @@
 
+struct VDPAUDeviceImpl VDPAUDeviceFunctions;
+
 static int queryOutputSurface(CtkVDPAU *ctk_vdpau, VdpDevice device,
--- a/nvidia-settings/src/gtk+-2.x/ctkvdpau.h
+++ b/nvidia-settings/src/gtk+-2.x/ctkvdpau.h
@@ -48,3 +48,3 @@
 
-struct VDPAUDeviceImpl {
+extern struct VDPAUDeviceImpl {