Link with libjbig when using built-in libtiff under Unix.

Link with libjbig when using built-in libtiff under Unix.

If libjbig is available, the built-in libtiff build process picks it up and
uses it, requiring all the code linking with libtiff to link with it too, so
add it to the list of the libraries in this case.

This is the same change as was already done for liblzma dependency in r74033,
see #14963.

Closes #15244.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74153 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775