test: make IDE.complete_with_multiple_imports work on Windows

`#import` has target dependent behaviour.  Rather than enabling ObjC
interop, switch to `#include` with include guards.  This permits the IDE
tests to fully pass on Windows.

Author: compnerd

test/IDE/Inputs/mock-sdk/FooHelper.framework/Frameworks/FooHelperSub.framework/Headers/FooHelperSub.h

@@ -1,3 +1,7 @@
+
+#ifndef FooHelperSub_FooHelperSub_h
+#define FooHelperSub_FooHelperSub_h
+
 int fooHelperSubFunc1(int a);
 
 enum FooHelperSubEnum1 {
@@ -9,3 +13,5 @@ enum {
   FooHelperSubUnnamedEnumeratorA1
 };
 
+#endif
+

test/IDE/Inputs/mock-sdk/FooHelper.framework/Headers/FooHelper.h

@@ -1,4 +1,8 @@
-#import <FooHelperSub/FooHelperSub.h>
+
+#ifndef FooHelper_FooHelper_h
+#define FooHelper_FooHelper_h
+
+#include <FooHelperSub/FooHelperSub.h>
 
 int fooHelperFunc1(int a);
 
@@ -7,3 +11,5 @@ enum {
   FooHelperUnnamedEnumeratorA2,
 };
 
+#endif
+