- add version info for v1.8.0

- v1.8.0 adds a new source file, `file.c`, which need to be included
  in our hardcoded list of objects to link.

  I discovered this while demonstrating "how easy it is to add a new
  package to Spack", only to scratch my head when it failed `spack
  install` but worked when I ran `make` in the stage dir.  Finally
  looked at tree/package.py and it All Became Clear.

  Perhaps someone should rewrite this to use MakefilePackage, but the
  Makefile starts off with a bunch of twisty turny "uncomment these
  lines to run on this platform", so it might not be worth it.