SwiftPrivate: correct dependencies on Windows

Ensure that we explicitly state the dependency on WinSDK to avoid issues
in parallel builds.  Caught by the Windows nightlies.

Author: compnerd

stdlib/private/SwiftPrivate/CMakeLists.txt

@@ -11,7 +11,7 @@ add_swift_target_library(swiftSwiftPrivate ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} I
   IO.swift
   ShardedAtomicCounter.swift
 
-  SWIFT_MODULE_DEPENDS_WINDOWS MSVCRT
+  SWIFT_MODULE_DEPENDS_WINDOWS MSVCRT WinSDK
   SWIFT_COMPILE_FLAGS ${swift_swiftprivate_compile_flags}
   INSTALL_IN_COMPONENT stdlib-experimental)