Log Message:
Make enchant2 bl3 create enchant.pc.

I have enough of these manual hacks in configure scripts that check for
'enchant => someversion' instead of 'enchant-2 >= someversion'. Instead,
let's give them the former.

Caveat: this makes it impossible to have enchant and enchant-2 buildlinked
into the same build, but you do not want that.