As icu 59 requires c++11, '-std=gnu++98' makes qtcore:4 fail icu check, yet (AFAIU) *all* qt libs need to be built with same std value. So, using current workaround, instead of importing patches from bugs noted in the eclass is likely no longer a valid solution.
There is no solution except disabling USE=icu for Qt4. Qt4 must die. *** This bug has been marked as a duplicate of bug 618638 ***