archivers/xmill: unbreak build with Clang 6 (C++14 by default)
./xmillinspect/exprinfo.cpp:64:10: error: cannot initialize return object of type 'int' with an rvalue of type 'nullptr_t'
return NULL; ^~~~
/usr/include/sys/_null.h:37:14: note: expanded from macro 'NULL'
#define NULL nullptr
^~~~~~~
Reported by: pkg-fallout