add dummied strverscmp (obnoxious GNU function)

programs that use this tend to horribly botch international text
support, so it's questionable whether we want to support it even in
the long term... for now, it's just a dummy that calls strcmp.

src/string/strverscmp.c

@@ -0,0 +1,7 @@
+#include <string.h>
+
+int strverscmp(const char *l, const char *r)
+{
+	/* FIXME */
+	return strcmp(l, r);
+}