[overlay] A tentative fix for the intermittent build failures.

It looks from the failed build logs that XCTest has a transitive
dependency on CoreMedia, so listing this dependency explicitly might
solve the problem.
rdar://problem/27404152

Author: Max Moiseev

stdlib/public/SDK/XCTest/CMakeLists.txt

@@ -7,7 +7,7 @@ add_swift_library(swiftXCTest ${SWIFT_SDK_OVERLAY_LIBRARY_BUILD_TYPES} IS_SDK_OV
   SWIFT_MODULE_DEPENDS ObjectiveC Foundation
   FRAMEWORK_DEPENDS Foundation XCTest
   SWIFT_MODULE_DEPENDS_OSX AppKit
-  SWIFT_MODULE_DEPENDS_IOS UIKit
+  SWIFT_MODULE_DEPENDS_IOS CoreMedia UIKit
   SWIFT_MODULE_DEPENDS_TVOS UIKit
   DONT_EMBED_BITCODE)