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

configure.in.in

@@ -1,5 +1,7 @@
 #MIN_CONFIG(3.3)
 
+KDE_ENABLE_HIDDEN_VISIBILITY
+
 # Remember to synchronize the version number with the file koffice/lib/kofficecore/kofficeversion.h
 AM_INIT_AUTOMAKE(koffice, "1.6.3")