If the linker suppors it, ensure that the library has no undefined
references.

This is important to make sure that no bugs are introduced that breaks
when using --as-needed.
diff --git a/configure.ac b/configure.ac
index 3078ab4..38b7701 100644
--- a/configure.ac
+++ b/configure.ac
@@ -70,6 +70,8 @@
 
 AC_SYS_LARGEFILE
 
+CC_NOUNDEFINED
+
 ZP_LYNX_DOC
 
 AC_ARG_ENABLE(examples,