swift234

Revert "Move the computation of generic signatures into the archetype builder."

This reverts commit r23030.

This puts non-primary archetypes back in the all-archetypes list,
which is the deepest underlying problem behind
rdar://problem/19049566.

Conflicts:
	lib/AST/ArchetypeBuilder.cpp
	validation-test/compiler_crashers/0033-error.swift
	validation-test/compiler_crashers/035-multiple-typecheck-segfault.swift

Swift SVN r24333