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/xregex.h b/include/xregex.h
index 23cf19c..d4bf732 100644
--- a/include/xregex.h
+++ b/include/xregex.h
@@ -12,7 +12,16 @@
 #define __BB_REGEX__
 
 #include <regex.h>
+
+#if __GNUC_PREREQ(4,1)
+# pragma GCC visibility push(hidden)
+#endif
+
 char* regcomp_or_errmsg(regex_t *preg, const char *regex, int cflags);
 void xregcomp(regex_t *preg, const char *regex, int cflags);
 
+#if __GNUC_PREREQ(4,1)
+# pragma GCC visibility pop
+#endif
+
 #endif