[test] Ensure clang importer sdk uses its own CoreFoundation overlay

We noticed that Some tests using the clang importer sdk ended up using the CoreFoundation overlay built as part of
Swift instead of the mock one provided.

Author: edymtt

test/IDE/print_clang_header_i386.swift

@@ -4,5 +4,7 @@
 // XFAIL: linux, freebsd
 
 // RUN: echo '#include "header-to-print.h"' > %t.i386.m
-// RUN: %target-swift-ide-test -source-filename %s -print-header -header-to-print %S/Inputs/print_clang_header/header-to-print.h -print-regular-comments --cc-args -arch i386 -isysroot %clang-importer-sdk-path -fsyntax-only %t.i386.m -I %S/Inputs/print_clang_header > %t.i386.txt
+// RUN: %empty-directory(%t)
+// RUN: %build-clang-importer-objc-overlays
+// RUN: %target-swift-ide-test -source-filename %s -print-header -header-to-print %S/Inputs/print_clang_header/header-to-print.h -print-regular-comments -I %t --cc-args -arch i386 -isysroot %clang-importer-sdk-path -fsyntax-only %t.i386.m -I %S/Inputs/print_clang_header > %t.i386.txt
 // RUN: diff -u %S/Inputs/print_clang_header/header-to-print.h.printed.txt %t.i386.txt

test/Inputs/clang-importer-sdk/swift-modules/CoreFoundation.swift

@@ -1,3 +1,3 @@
 @_exported import CoreFoundation
 
-protocol _CFObject {}
+protocol _CFObject: Hashable {}

test/lit.cfg

@@ -459,6 +459,7 @@ config.substitutions.append( ('%clang-include-dir', config.clang_include_dir) )
 config.substitutions.append(('%build-clang-importer-objc-overlays',
                              '%target-swift-frontend(mock-sdk: %clang-importer-sdk-nosource -I %t) -enable-objc-interop -emit-module -o %t %clang-importer-sdk-path/swift-modules/ObjectiveC.swift -disable-objc-attr-requires-foundation-module && '
                              '%target-swift-frontend(mock-sdk: %clang-importer-sdk-nosource -I %t) -enable-objc-interop -emit-module -o %t %clang-importer-sdk-path/swift-modules/CoreGraphics.swift && '
+                             '%target-swift-frontend(mock-sdk: %clang-importer-sdk-nosource -I %t) -enable-objc-interop -emit-module -o %t %clang-importer-sdk-path/swift-modules/CoreFoundation.swift && '
                              '%target-swift-frontend(mock-sdk: %clang-importer-sdk-nosource -I %t) -enable-objc-interop -emit-module -o %t %clang-importer-sdk-path/swift-modules/Foundation.swift'))
 
 # FIXME: BEGIN -enable-source-import hackaround