Declaration taken from nss sources' lib/softoken/pkcs11i.h.
Only needed with --enable-pk11install.

https://bugs.gentoo.org/871585
--- a/src/install/pk11install.c
+++ b/src/install/pk11install.c
@@ -23,4 +23,6 @@
 #include "pkcs11n.h"
 
+char **NSC_ModuleDBFunc(unsigned long function, char *parameters, void *args);
+
 /*
  * windows specific globing search