fix macro issue reported by Vladimir Menshakov

git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@9044 626c5289-ae23-0410-ae9c-e8d60b6d4f22

Lib/linkruntime.c

@@ -1,3 +1,4 @@
+#ifndef SWIGEXPORT
 # if defined(_WIN32) || defined(__WIN32__) || defined(__CYGWIN__)
 #   if defined(STATIC_LINKED)
 #     define SWIGEXPORT
@@ -5,6 +6,13 @@
 #     define SWIGEXPORT __declspec(dllexport)
 #   endif
 # else
+#   if defined(__GNUC__) && defined(GCC_HASCLASSVISIBILITY)
+#     define SWIGEXPORT __attribute__ ((visibility("default")))
+#   else
+#     define SWIGEXPORT
+#   endif
+# endif
+#endif
 
 static void *ptr = 0;
 SWIGEXPORT void *