Add automake support for --enable-gcc-hidden-visibility.

configure.in.in

@@ -1,6 +1,8 @@
 #MIN_CONFIG(3.3.0)
 #AM_KDE_MIN_VERSION(3.3.0)
 
+KDE_ENABLE_HIDDEN_VISIBILITY
+
 AM_INIT_AUTOMAKE(smb4k,0.9.4)