Add fixed crasher to close swiftlang#43442

Author: AnthonyLatsis

validation-test/compiler_crashers_2_fixed/issue43442.swift

@@ -0,0 +1,13 @@
+// RUN: %target-swift-frontend %s -typecheck
+
+// https://github.com/apple/swift/issues/43442
+
+func quickSort<T: Comparable>(_ a: [T]) -> [T] {
+  if a.isEmpty {
+    return a
+  } else {
+    let head = a[0]
+    let body = a[1..<a.count]
+    return quickSort(body.filter({$0 < head})) + [head] + quickSort(body.filter({$0 >= head}))
+  }
+}