>>> /usr/lib64/pkgconfig/nss.pc
>>> Safely unmerging already-installed instance...
Traceback (most recent call last):
  File "/usr/bin/emerge", line 4358, in ?
    retval = emerge_main()
  File "/usr/bin/emerge", line 4353, in emerge_main
    myopts, myaction, myfiles, spinner)
  File "/usr/bin/emerge", line 3833, in action_build
    retval = mergetask.merge(
  File "/usr/bin/emerge", line 2287, in merge
    prev_mtimes=ldpath_mtimes)
  File "/usr/lib/portage/pym/portage.py", line 3128, in doebuild
    vartree=vartree, prev_mtimes=prev_mtimes)
  File "/usr/lib/portage/pym/portage.py", line 3347, in merge
    mydbapi=mydbapi, prev_mtimes=prev_mtimes)
  File "/usr/lib/portage/pym/portage.py", line 6619, in merge
    cleanup=cleanup, mydbapi=mydbapi, prev_mtimes=prev_mtimes)
  File "/usr/lib/portage/pym/portage.py", line 6273, in treewalk
    self.unmerge(oldcontents, trimworld=0, ldpath_mtimes=prev_mtimes)
  File "/usr/lib/portage/pym/portage.py", line 5851, in unmerge
    self.settings, 0, 0, self.vartree.dbapi)
  File "/usr/lib/portage/pym/portage.py", line 2614, in doebuild_environment
    raise portage_exception.UnsupportedAPIException(mycpv, eapi)