Add KDE_EXPORT to public library symbols.

This allows build with gcc hidden visibility.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit 41ffd4d2f7)

settings-backend/tdeconfig_backend.cpp

@@ -1963,7 +1963,7 @@ static CCSBackendVTable tdeconfigVTable =
 extern "C"
 {
 
-    CCSBackendVTable *
+    KDE_EXPORT CCSBackendVTable *
     getBackendInfo (void)
     {
 	return &tdeconfigVTable;