swiftStdlibCollectionUnittest needed by check-swift-validation-only_executable-freestanding-x86_64 and no known rule to make it

Missed some dependencies of the private stdlib pieces that are only available when the SDK overlay is available.

rdar://135878323

Author: ian-twilightcoder

test/CMakeLists.txt

@@ -333,9 +333,17 @@ foreach(SDK ${SWIFT_SDKS})
         list(APPEND test_dependencies "touch-covering-tests")
       endif()
 
-      list(APPEND test_dependencies
-        "swiftStdlibCollectionUnittest-${SWIFT_SDK_${SDK}_LIB_SUBDIR}"
-        "swiftStdlibUnicodeUnittest-${SWIFT_SDK_${SDK}_LIB_SUBDIR}")
+      # Keep in sync with stdlib/private/CMakeLists.txt: the private stdlib
+      # targets all rely on the SDK overlay being available.
+      if(SWIFT_BUILD_SDK_OVERLAY
+         OR (SWIFT_BUILD_TEST_SUPPORT_MODULES
+             AND NOT SWIFT_BUILD_DYNAMIC_SDK_OVERLAY_default
+             AND (SWIFT_ENABLE_REFLECTION
+                  OR NOT SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS)))
+        list(APPEND test_dependencies
+          "swiftStdlibCollectionUnittest-${SWIFT_SDK_${SDK}_LIB_SUBDIR}"
+          "swiftStdlibUnicodeUnittest-${SWIFT_SDK_${SDK}_LIB_SUBDIR}")
+      endif()
 
       set(validation_test_dependencies)