OSX 10.10.5 Symbol not found: _XML_SetHashSalt, Expected in: /usr/lib/libexpat.1.dylib

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

Building devel/py-appdirs on my 10.10.5 fails with

ImportError: dlopen(/usr/pkg/lib/python2.7/lib-dynload/pyexpat.so, 2): Symbol not found: _XML_SetHashSalt
  Referenced from: /usr/pkg/lib/python2.7/lib-dynload/pyexpat.so
  Expected in: /usr/lib/libexpat.1.dylib
 in /usr/pkg/lib/python2.7/lib-dynload/pyexpat.so

I guess that's #520 XML_SetHashSalt not exported? (https://sourceforge.net/p/expat/bugs/520/) or the expat verson bundled with OSX 10.10 is too old altogether.

I'm not very familiar with the builtin/buildlink3 framework, but I guess the solution is to find out which versions of OSX have a libexpat lacking that symbol and building expat from pkgsrc on those.