While trying to emerge qtcore-4.8.6-r2 or -4.8.7-r2 build fails during preparation with message

• ERROR: dev-qt/qtcore-4.8.7-r2::gentoo failed (prepare phase):
• USE Flag 'ia64-linux' not in IUSE for dev-qt/qtcore-4.8.7-r2
  qtcore-4.8.6-r2 fails with the same error
  ia-64-linux is not used anywhere in the system, neither in global, per-package use flags nor in system profile. Adding -ia64-linux to global use flag does not fix the problem. Complete build log attached in qtcore_buildlog.txt.
  Also, qtcore-5.7.1 builds without any problems on the same system.