[coreVdpau] Try to load VDPAU library by versioned symlink

The unversioned symlink libvdpau.so belongs to the devel package at least on
Debian and derivatives as well as on Fedora and therefore is usually missing.

avidemux_core/ADM_coreVideoCodec/ADM_hwAccel/ADM_coreVdpau/src/ADM_coreVdpau.cpp

@@ -102,10 +102,13 @@ VdpGetProcAddress        *admVdpau::getProcAddress2(void)
 */
 bool admVdpau::init(GUI_WindowInfo *x)
 {
+#define STR(x) #x
+#define MKSTRING(x) STR(x)
+#define VDPAU_LIBNAME libvdpau.so.1
     memset(&ADM_coreVdpau::funcs,0,sizeof(ADM_coreVdpau::funcs));
-    if(false==vdpauDynaLoader.loadLibrary("libvdpau.so"))
+    if(false==vdpauDynaLoader.loadLibrary(MKSTRING(VDPAU_LIBNAME)))
     {
-        ADM_info("Cannot load libvdpau.so\n");
+        ADM_info("Cannot load " MKSTRING(VDPAU_LIBNAME) "\n");
         return false;
     }
     ADM_createVdpX11=(VdpDeviceCreateX11*)vdpauDynaLoader.getSymbol("vdp_device_create_x11");