[NFC] Add test for self-cycles in module trace.

Author: varungandhi-apple

test/Driver/Inputs/imported_modules/SelfImport/module.modulemap

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+module Outer {
+ module Inner {
+  export Outer.Inner
+ }
+ export Outer
+}

test/Driver/loaded_module_trace_self_cycle.swift

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+// Check that this doesn't crash due to a self-cycle. rdar://67435472
+// RUN: not --crash %target-swift-frontend %s -emit-module -o /dev/null -emit-loaded-module-trace-path /dev/null -I %S/Inputs/imported_modules/SelfImport
+
+import Outer