1. Resolve the "hidden symbol 'atexit' ... being referenced by DSO" error
   by using the -shared option (link against shared objects, not static libs)
2. The path to the xpdev output directory (where to find libxpdev.a) is just
   wrong. Hard-coded the machine architecuture portion (.x64) as a hack for
   now. Also, since this is use the LD macro, you need to pass "LD=gcc" on the
   make command-line. Not sure how this worked before.

Fixes (or at least works-around) issues reported by Ryan Fantus (1:218/820)