disable servant build flag for i386ancient

disable servant build flag for i386ancient

Its library stack is too old, and while lts-12.14 does include an old
version of servant, some libraries like http-client have been bumped up
from the lts to support eg http-client-restricted. So a newer servant
would be needed, which would lead to many more upgrades.

There might be a dependency set that works, but I have not been able to
find it so far. stack solver also failed to find one.