build: add a workaround for reflection test on Windows

Copy the runtime component into the swift runtime directory.  Normally
the runtime directory is not the same as the library directory on
Windows.  This copies the runtime component into the build tree into the
runtime directory to permit the tests to find the standard library.

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -1027,6 +1027,11 @@ function(_add_swift_library_single target name)
     set_target_properties("${target}" PROPERTIES
       LIBRARY_OUTPUT_DIRECTORY ${SWIFTLIB_DIR}/${SWIFTLIB_SINGLE_SUBDIR}
       ARCHIVE_OUTPUT_DIRECTORY ${SWIFTLIB_DIR}/${SWIFTLIB_SINGLE_SUBDIR})
+    if(SWIFTLIB_SINGLE_SDK STREQUAL WINDOWS AND SWIFTLIB_SINGLE_IS_STDLIB_CORE
+        AND libkind STREQUAL SHARED)
+      add_custom_command(TARGET ${target} POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different $<TARGET_FILE:${target}> ${SWIFTLIB_DIR}/${SWIFTLIB_SINGLE_SUBDIR})
+    endif()
 
     foreach(config ${CMAKE_CONFIGURATION_TYPES})
       string(TOUPPER ${config} config_upper)