[test] Make sure we don't try to autolink the framework we're building (swiftlang#20245)

...even the Clang part of it.

rdar://problem/42604464

Author: jrose-apple

test/ClangImporter/MixedSource/Inputs/AutolinkingTest.framework/AutolinkingTest

@@ -0,0 +1,3 @@
+struct Test {
+  int value;
+};

test/ClangImporter/MixedSource/Inputs/AutolinkingTest.framework/Headers/AutolinkingTest.h

@@ -0,0 +1,5 @@
+framework module AutolinkingTest {
+  umbrella header "AutolinkingTest.h"
+  export *
+  module * { export * }
+}

test/ClangImporter/MixedSource/Inputs/AutolinkingTest.framework/Modules/module.modulemap

@@ -0,0 +1,16 @@
+// RUN: %target-swift-frontend %s -module-name AutolinkingTest -F %S/Inputs -import-underlying-module -emit-ir | %FileCheck %s
+
+// Linux uses a different autolinking mechanism, based on
+// swift-autolink-extract. This file tests the Darwin mechanism.
+// UNSUPPORTED: OS=linux-gnu
+// UNSUPPORTED: OS=linux-gnueabihf
+// UNSUPPORTED: OS=freebsd
+// UNSUPPORTED: OS=linux-androideabi
+
+// Use a type declared in the Clang part of the module.
+public let y = Test()
+
+// CHECK: !llvm.linker.options
+// CHECK-NOT: !{!"-framework", !"AutolinkingTest"}
+// CHECK: !{!"-lswiftCore"}
+// CHECK-NOT: !{!"-framework", !"AutolinkingTest"}