wxGTK: Using built-in libtiff may need to link to libjbig too

[dghart]

#14963 reported that, when wx was configured --with-libtiff=builtin in the presence of liblzma-dev, wx needed to link -llzma; otherwise programs linking to libwx_gtk2u_core-2.9 would get 'undefined reference' errors. Changeset 74033 fixed this.

I've now found an analogous situation with built-in libtiff if libjbig-dev is present. The attached patch fixes this in the same way.

[VZ]

(In [74153]) 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.