context: Add support for [per-thread] global talloc contexts

Rather than having applications maintain their own talloc cotexts,
let's offer some root talloc contexts in libosmocore.  Let's also
make them per thread right from the beginning.  This will help
some multi-threaded applications to use talloc in a thread-safe
way.

Change-Id: Iae39cd57274bf6753ecaf186f229e582b42662e3
diff --git a/include/osmocom/core/select.h b/include/osmocom/core/select.h
index e4787b0..a200b6f 100644
--- a/include/osmocom/core/select.h
+++ b/include/osmocom/core/select.h
@@ -51,6 +51,7 @@
 void osmo_fd_unregister(struct osmo_fd *fd);
 void osmo_fd_close(struct osmo_fd *fd);
 int osmo_select_main(int polling);
+int osmo_select_main_ctx(int polling);
 
 struct osmo_fd *osmo_fd_get_by_fd(int fd);