re PR go/54918 (libgo.so.0 is not runtime compatible between gcc-4.6.2 and gcc-4.7.x)

	PR go/54918
libgo: Set library version number.

From-SVN: r192706
diff --git a/libgo/configure.ac b/libgo/configure.ac
index 217763d..8cde50b 100644
--- a/libgo/configure.ac
+++ b/libgo/configure.ac
@@ -11,7 +11,7 @@
 AC_CONFIG_SRCDIR(Makefile.am)
 AC_CONFIG_HEADER(config.h)
 
-libtool_VERSION=1:0:0
+libtool_VERSION=3:1:0
 AC_SUBST(libtool_VERSION)
 
 AM_ENABLE_MULTILIB(, ..)