[Sema] Fix isCanonical calculation in FunctionType::get.

Fixes rdar://problem/57644243.

Author: varungandhi-apple

lib/AST/ASTContext.cpp

@@ -3008,8 +3008,12 @@ FunctionType *FunctionType::get(ArrayRef<AnyFunctionType::Param> params,
   void *mem = ctx.Allocate(allocSize, alignof(FunctionType), arena);
 
   bool isCanonical = isFunctionTypeCanonical(params, result);
-  if (uncommon.hasValue())
-    isCanonical &= uncommon->ClangFunctionType->isCanonicalUnqualified();
+  if (uncommon.hasValue()) {
+    if (ctx.LangOpts.UseClangFunctionTypes)
+      isCanonical &= uncommon->ClangFunctionType->isCanonicalUnqualified();
+    else
+      isCanonical = false;
+  }
 
   auto funcTy = new (mem) FunctionType(params, result, info,
                                        isCanonical ? &ctx : nullptr,

test/Sema/clang_types_in_ast.swift

@@ -4,8 +4,9 @@
 // RUN: %target-swift-frontend %s -typecheck -DNOCRASH2 -sdk %clang-importer-sdk
 // RUN: %target-swift-frontend %s -typecheck -DNOCRASH2 -sdk %clang-importer-sdk -use-clang-function-types
 // RUN: %target-swift-frontend %s -DAUXMODULE -module-name Foo -emit-module -o %t
-// FIXME: rdar://problem/57644243 : We shouldn't crash if -use-clang-function-types is not enabled.
-// RUN: not --crash %target-swift-frontend %s -typecheck -DNOCRASH3 -I %t
+
+// rdar://problem/57644243 : We shouldn't crash if -use-clang-function-types is not enabled.
+// RUN: %target-swift-frontend %s -typecheck -DNOCRASH3 -I %t
 
 // FIXME: [clang-function-type-serialization] This should stop crashing once we
 // start serializing clang function types.