[REG2.063] fix issue 10456 - struct containing enum X, alias X this and a dynamic array no longer compiles since 2.063

http://d.puremagic.com/issues/show_bug.cgi?id=10456

Caused by https://github.com/D-Programming-Language/dmd/commit/5a1307007cd033386ec3d31c70118deaaeb7ff51, I guess.