Re-added case marked as crashed.

Reliably crashes swift-ide-test compiled from current master.

See discussion in #607 and previously #587.

Author: practicalswift

validation-test/IDE/crashers/024-swift-archetypebuilder-potentialarchetype-getrepresentative.swift

@@ -0,0 +1,4 @@
+// RUN: not --crash %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+protocol c{func a:P
+protocol P{#^A^#func a:b
+typealias b:a