lib: Introduce versioned symbols

As rpm-ostree evolves, it keeps driving API additions to libostree.
This creates a relatively tight coupling.

However, if delivering via e.g. RPM, unless one manually remembers to
increment the `Requires:` in the spec file, it's possible for the two
to become desynchronized.

RPM handles versioned symbols and will ensure a dependency if the
application starts using a newer version.

To implement this, switch to `-fvisibility=hidden`, along with an
annotation in the header, and finally add a `.sym` file.

This matches what other projects like systemd and libvirt do.

Although rather than attempting to retroactively version symbols, glom
them all onto the current one.

src/libostree/ostree-async-progress.h

@@ -41,29 +41,39 @@ struct OstreeAsyncProgressClass
   void (*changed) (OstreeAsyncProgress *self, gpointer user_data);
 };
 
+_OSTREE_PUBLIC
 GType   ostree_async_progress_get_type (void) G_GNUC_CONST;
 
+_OSTREE_PUBLIC
 OstreeAsyncProgress *ostree_async_progress_new (void);
 
+_OSTREE_PUBLIC
 OstreeAsyncProgress *ostree_async_progress_new_and_connect (void (*changed) (OstreeAsyncProgress *self, gpointer user_data), gpointer user_data);
 
+_OSTREE_PUBLIC
 char *ostree_async_progress_get_status (OstreeAsyncProgress       *self);
 
+_OSTREE_PUBLIC
 guint ostree_async_progress_get_uint (OstreeAsyncProgress       *self,
                                       const char                *key);
+_OSTREE_PUBLIC
 guint64 ostree_async_progress_get_uint64 (OstreeAsyncProgress       *self,
                                           const char                *key);
 
+_OSTREE_PUBLIC
 void ostree_async_progress_set_status (OstreeAsyncProgress       *self,
                                        const char                *status);
 
+_OSTREE_PUBLIC
 void ostree_async_progress_set_uint (OstreeAsyncProgress       *self,
                                      const char                *key,
                                      guint                      value);
+_OSTREE_PUBLIC
 void ostree_async_progress_set_uint64 (OstreeAsyncProgress       *self,
                                        const char                *key,
                                        guint64                    value);
 
+_OSTREE_PUBLIC
 void ostree_async_progress_finish (OstreeAsyncProgress *self);
 
 G_END_DECLS