[ModuleTrace] Early exit if a Clang module imports itself.

Fixes rdar://67435472.

Author: varungandhi-apple

lib/FrontendTool/FrontendTool.cpp

@@ -588,8 +588,9 @@ void ABIDependencyEvaluator::computeABIDependenciesForClangModule(
     }
     if (import->isNonSwiftModule()
         && module->getTopLevelModule() == import->getTopLevelModule()
-        && !import->findUnderlyingClangModule()
-                  ->isSubModuleOf(module->findUnderlyingClangModule())) {
+        && (module == import
+            || !import->findUnderlyingClangModule()
+                      ->isSubModuleOf(module->findUnderlyingClangModule()))) {
       continue;
     }
     computeABIDependenciesForModule(import);

test/Driver/loaded_module_trace_self_cycle.swift

@@ -1,4 +1,4 @@
 // 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
+// RUN: %target-swift-frontend %s -emit-module -o /dev/null -emit-loaded-module-trace-path /dev/null -I %S/Inputs/imported_modules/SelfImport
 
 import Outer