Use intra-DSO calls when we build libbusybox. No-op for normal build.
This was Bernhard Fischer' idea.

   text    data     bss     dec     hex filename
 773549    7781    9740  791070   c121e busybox.t7/0_lib/libbusybox.so.1.11.0.svn_unstripped
 769683    7397    9740  786820   c0184 busybox.t9t/0_lib/libbusybox.so.1.11.0.svn_unstripped

diff --git a/include/xatonum.h b/include/xatonum.h
index 49ddced..6cf1299 100644
--- a/include/xatonum.h
+++ b/include/xatonum.h
@@ -7,6 +7,10 @@
  * Licensed under GPLv2, see file LICENSE in this tarball for details.
  */
 
+#if __GNUC_PREREQ(4,1)
+# pragma GCC visibility push(hidden)
+#endif
+
 /* Provides extern declarations of functions */
 #define DECLARE_STR_CONV(type, T, UT) \
 \
@@ -166,3 +170,7 @@
 /* Floating point */
 
 /* double bb_strtod(const char *arg, char **endp); */
+
+#if __GNUC_PREREQ(4,1)
+# pragma GCC visibility pop
+#endif