[test] Clean up two importer+serialization tests.

...and give them a proper "REQUIRES: objc_interop" instead of "XFAIL: linux".

Author: jrose-apple

test/ClangModules/Inputs/SerializationHelper.swift

@@ -1,5 +1,3 @@
-import Foundation
-
 @_exported import ProtoWithInitializer
 @_exported import TypeAndValue
 

test/ClangModules/serialization-search-paths.swift

@@ -1,8 +1,8 @@
 // RUN: rm -rf %t && mkdir -p %t
-// RUN: %target-swift-frontend -emit-module-path %t/SerializationHelper.swiftmodule -I %S/Inputs/custom-modules -F %S/Inputs/frameworks %S/Inputs/SerializationHelper.swift
-// RUN: %target-swift-frontend -parse -I %t %s -verify
+// RUN: %target-swift-frontend -emit-module-path %t/SerializationHelper.swiftmodule -I %S/Inputs/custom-modules -F %S/Inputs/frameworks -sdk "" -disable-objc-attr-requires-foundation-module %S/Inputs/SerializationHelper.swift
+// RUN: %target-swift-frontend -parse -I %t %s -sdk "" -verify
 
-// XFAIL: linux
+// REQUIRES: objc_interop
 
 import SerializationHelper
 import Module

test/ClangModules/serialization.swift

@@ -1,9 +1,9 @@
 // RUN: rm -rf %t
 // RUN: mkdir -p %t
-// RUN: %target-swift-frontend -emit-module-path %t/SerializationHelper.swiftmodule -I %S/Inputs/custom-modules %S/Inputs/SerializationHelper.swift
-// RUN: %target-swift-frontend -parse -I %t -I %S/Inputs/custom-modules %s -verify
+// RUN: %target-swift-frontend -emit-module-path %t/SerializationHelper.swiftmodule -I %S/Inputs/custom-modules %S/Inputs/SerializationHelper.swift -sdk "" -disable-objc-attr-requires-foundation-module
+// RUN: %target-swift-frontend -parse -sdk "" -I %t -I %S/Inputs/custom-modules %s -verify
 
-// XFAIL: linux
+// REQUIRES: objc_interop
 
 import SerializationHelper