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

e2fsprogs/e2fs_lib.h

@@ -9,6 +9,10 @@
 /* Constants and structures */
 #include "e2fs_defs.h"
 
+#if __GNUC_PREREQ(4,1)
+# pragma GCC visibility push(hidden)
+#endif
+
 /* Iterate a function on each entry of a directory */
 int iterate_on_dir(const char *dir_name,
 		int (*func)(const char *, struct dirent *, void *),
@@ -41,3 +45,7 @@ extern const char e2attr_flags_sname[];
 #define e2attr_flags_value_chattr (&e2attr_flags_value[1])
 #define e2attr_flags_sname_chattr (&e2attr_flags_sname[1])
 #endif
+
+#if __GNUC_PREREQ(4,1)
+# pragma GCC visibility pop
+#endif