[test] Disable two more collection tests in unoptimized builds

Author: lorentey

validation-test/stdlib/Collection/FlattenCollection.swift.gyb

@@ -2,6 +2,10 @@
 // RUN: %target-run-simple-swiftgyb
 // REQUIRES: executable_test
 
+// FIXME: the test is too slow when the standard library is not optimized.
+// rdar://problem/46878013
+// REQUIRES: optimized_stdlib
+
 import SwiftPrivate
 import StdlibUnittest
 import StdlibCollectionUnittest

validation-test/stdlib/Collection/LazyFilterCollection.swift.gyb

@@ -2,6 +2,10 @@
 // RUN: %target-run-simple-swiftgyb
 // REQUIRES: executable_test
 
+// FIXME: the test is too slow when the standard library is not optimized.
+// rdar://problem/46878013
+// REQUIRES: optimized_stdlib
+
 import SwiftPrivate
 import StdlibUnittest
 import StdlibCollectionUnittest